The Tanganyika problem; an account of the researches undertaken concerning the existence of marine animals in Central Africa

Preface

In completing the present account of the researches which were undertaken during the two Tanganyika expeditions, I am somewhat oppressed with the possibility that the unique opportunities and material available may not have received the justice they would have done in the hands of many naturalists who have more experience than I am old enough to possess. We were actually the last zoological explorers with a great untouched field before them, and when it is remembered, that among other things, we have had to deal with nearly 200* entirely new animal types discovered during these expeditions, it will be admitted that the labour of giving an adequate account of the faunistic characters of the great African lakes has not been exactly child’s play. It should, moreover, be clearly understood that the acquisition of all this new material and information respecting Central Africa has been primarily due to the instigation and persistence of Professor Ray Lankester, and I only wish that he, instead of myself, could have found time to write the present account. On the other hand, it would perhaps have been impossible for anyone who was without a somewhat prolonged and actual acquaintance with the African interior, to attempt to deal with all the aspects the Tanganyika problem has been found to present, and I can therefore only point out to any who may feel that the present work could have been better done, that I am fully conscious of its peculiar deficiencies.

Few people here, moreover, will be able to appreciate how completely during the actual operations of exploring parties in practically unknown countries, whatever results may be obtained are due to the disinterested and gratuitous help which may or may not be extended to them by people, administrators and the like, who live

* In this connection it may be interesting to remember that the whole of the fishes, fresh water and marine, belonging to the British Islands, only represent about 240 species.

VI

THE TANGANYIKA TROBLEM.

upon the borders of such unknown lands. In the present case, all our results with respect to the fauna and topography of Xvassa, and much of the efficiency of the expedition further north, was due to the efforts of H.M. Commissioner, Mr. Alfred Sharpe, who allowed me to examine the lake from the gunboats, and facilitated our journey in many ways as far as the northern boundary of the British Central African Protectorate. In this way we were able to ascertain the actual depth of Lake Nyassa— 430 fathoms — a result which is sufficiently surprising, and one which, I am happy to say, has since been closely confirmed in an adjacent area by Commander Rhoades. In like manner we received much help in the selection of men and kindness generally from General Creagh, the British Resident at Aden ; from Mr. Codrington in Northern Rhodesia ; and perhaps I might also say we have been particularly indebted to Captain Bethe, and his brother officers in command of the German territory north and east of Tanganyika. In the later stages of the journey a great quantity of animals in spirit, and what remained of things in general, were hurried safely through Uganda to the coast by the help of H.M. Commissioner Mr. Jackson and Mr. Pordage at Mtebi.

Turning from these details of the route to the subject of the investigations themselves, I should say at once that all the geographical work, which has resulted in the first effective mapping of the region that had so long remained in dispute between Tanganyika and the Albert Nyanza, has been due to the energy and skill of my colleague Mr. I'ergusson, and in like manner much of the geological data with which I have had to deal in the sequel was originally collected and arranged by him.

The revision of the existing geological conceptions of the African interior, which the information obtained during the Tanganyika Expeditions necessitates, will possibly be found the most generally interesting result that these investigations have produced. It will be seen in the succeeding chapters that the whole of our current views of the geological nature of the Continent are radically unsound and incorrect. It can indeed be shown that even Suess’ conception of the graben (rift valleys) by no means always expresses the actual structure of these remarkable depressions, they are far better described under the title of

PREFACE.

vii

“ Eurycolpic folds,” a term recently suggested to me, and which I have intentionally introduced into the present work in preference to either “ graben,” or “ rift valleys,” both of which are obviously misnomers, since the valleys in question are generally produced by folding, due to lateral pressure, and not either through rifting, or vertical collapse.

Since our return, and in connection with both the first and second Tanganyika expeditions, the large number of new fishes obtained have been elaborately worked out by Mr. Boulenger of the British Museum. The descriptions contained in the present volume being his simply, while the more conspicuous genera and species have been accurately illustrated by Mr. Green. The Crustacea were examined by Messrs. Cunnington and Caiman, the Sponges by Mr. Evans, Professor Minchin and Herr Weltner in Berlin. For the description of the Mollusca, the Polyzoa and Protozoa, I myself have been responsible, but I have received unlimited help from Professor Ray Lankester himself, Mr. Edgar Smith and others at the British Museum. The anatomy of the celebrated jelly-fish was examined some years ago by Mr. Gunther in Oxford, and in what appears in the present volume, I have consequently been able to draw largely upon his original description, only adding some drawings of the living Medusa together with information about its life history and development, which I acquired on the spot. We have been further indebted to Mr. Prior for the complete identification of the rock specimens collected by Mr. Fergusson ; and, as 1 have explained in the text, we have been most materially helped by Mr. Huddleston in the comparison of the Tanganyika gastropods with the shell remains of the Jurassic seas. Last, but not least, I have to thank Professor G. B. Howes, who after my return from both my first and second Tanganyika expeditions, allowed me the unlimited use of the Huxley laboratory in the Royal College of Science and of his own experience and advice.

The title which I have chosen for the present work, “ The Tanganyika Problem,” expresses the fact that there is a puzzle, a mystery, attached to Tanganyika, and the elucidation of this mystery has formed the single motive for several independent lines of enquiry described in the present volume. The Tan-

THE TANGANYIKA PROBLEM.

viii

ganyika problem thus lends itself to the formation of a connected story, and I can point out to the general reader, who may be attracted to the puzzle as he would be to a cock-fight, that he need not be alarmed at technicalities to follow, these having been intentionally rendered conspicuous for omission in small type. Moreover to those who know Africa, I think it may be positively refreshing to find that the interior has actually got some attributes besides a continued absence of gold, and a total unsuitability for European colonization. Further, since the present volume contains the only general, illustrated account of the animals found in the great lakes, it is hoped that it may be really of use to numbers of people, who in spite of attributes, still go out to the African interior, but who up to the present time have had no means of ascertaining the nature of the sometimes extremely good fishes they are continually eating.

Of the manner in which the second Tanganyika expedition was organised, and of the method of treating the Tanganyika problem which I have adopted in the present volume, it is not necessary to speak. I have already dealt with these matters in the introductory chapters ; but I may point out that I have intentionally introduced as many illustrations and photographs of the localities described as possible, since it seems to me that no one can form any clear idea of the physical characters of an extensive area from maps and descriptions alone. So again, in chapter six, I have re-introduced matter relating to the formation of Park lands upon alluvial flats, which I had already published in a former work ; while lastly, owing to a misapprehension under which Sir Harry Johnston labours with respect to the relation of his own to other explorations in the Mountains of the Moon, I have had to refer to this range at greater length than I originally intended ; but I do not wish it to be understood that I undervalue Sir Harry’s work in this direction ; on the contrary, I think it distinctly interesting and valuable, since, although he did not reach a?- high an altitude as myself, in all major points he has completely confirmed the results which I had previously attained.

October , 1902,

Londoti.

Chapter I. Introductory

PAGE

Reasons for acquiring a better knowledge of the fauna of the Great African Lakes —

Our first knowledge of the existence of unique animals in Tanganyika arose as a by product of Burton’s journey — The shells collected by Speke on Tanganyika were marine in aspect — But the shells obtained from the other African Lakes were not so — Extension of our knowledge of the Tanganyika shells — Possibility of the lake having been connected with the sea — Intensification of the interest in the Tanganyika problem produced by Boehm’s discovery of jelly-fishes — • Formation of the first Tanganyika expedition — As a result of this it is shown that the Tanganyika problem is larger than was supposed — Conflict between the zoological evidence and geological anticipations — Erroneous character of Murchison’s geological speculations — Actual impressions of the African interior— Remarkable character of the Halolimnic shells of Tanganyika — Their similarity to those of the Jurassic seas — This comparison a possible solution of the Tanganyika problem — Insufficiency of our knowledge of the Great African Lakes — Suess’ views — Possibility of a former extension of the sea into Tanganyika from the north — Geological and geographical interest of the country north of Tanganyika — Formation of the second Tanganyika expedition — Arrangement of matters contained in the present work ..... I

CHAPTER IE

ON THE NATURE AND ORIGIN OF FRESH-WATER FAUNAS AND THEIR RELATION TO THE FAUNA OF THE SEA.

Animals live in fresh-water which do not inhabit the sea — Animals live also in brackish water — It is generally accepted that fresh-water organisms have arisen from marine forms and have colonized fresh-waters from the ocean — Recent additions to our knowledge of fresh-water faunas — Beaudants’ experiments— Views of Semper Sollas and Von Martens — Apparent impossibility of many marine organisms eyer getting into fresh-water — Inadequacy of existing views respecting the nature of fresh-water faunas — Similarity of fresh-water faunas all over the world — Distinction of primary and secondary fresh-water stocks — Origin of the second obvious, of the first not so clear — Ancestral

X

THE TANGANYIKA TROT LEM.

PAGE

characters of primary fresh water stocks — Palaeontological record of the appearance of the primary fresh-water stocks — This, synchronous with other geological phenomena — The universal distribution of the primary fresh-water stock inexplicable on the assumption of migration — Want of evidence of any capacity for migration — The zoological facts seem to suggest a former difference in the sea itself — Increase of salt in fresh-water shown to be prejudical to certain animals — Effects of this as exhibited in Lake Shirwa — Artificial production of similar results — Experiments of Loeb, Ilerbst, and others, show that a change in the character of sea-water may produce variation — General evidence for a continually increasing salinity in the sea — The action of this in the production of modern fresh-water faunas — Present view of the nature of fresh-water faunas .............. 1 1

Chapter III. The Physiographical Features Of The African Interior

THE GREAT CENTRAL RANGE.

Necessity of a knowledge of the topography of the Great Lake Region — Our views are changing with respect to the interior — Recent observations lend no support to the older conceptions which sprang from Murchison’s erroneous hypothesis respecting African stability — Demonstration of the existence of a Great Central Range a chief result of the Tanganyika expeditions — Characters of this range — Scott Elliot’s early appreciation of its existence — The east and west drainage slopes — The existence of deep valleys (Eurycolpic folds) parallel with the range — These, rock valleys, not formed by ice — Disturbance of old aqueous deposits, caused by the formation of the Great Central Range — Character of the Great Central Range in the region of Nyassa — Absence of true volcanoes along the ridges of the range — Wide effects of the formation of the Great Central Range — The “graben” of Suess ; Eurycolpic folds — Characters of these folds in the region of Nyassa — Characters of the folds in the region of Tanganyika— Disturbance of the valleys and ridges in relation to the Great Central Range ............ 31

Chapter IV. Superficial Geology Of The Region Of The Great African Lakes

Evidence respecting the nature of the central African region before the formation of the Great Central Range — Continuation of the movements which have produced the Great Central Range — Recent discover)- of vast aqueous deposits in the interior — Value of these in ascertaining the past history of the continent — Method of treating the subject in relation to the observations made during the Tanganyika expeditions — Vastness of the regions to be considered — Character of the southern section of the region of the Great African Lakes — Nature of

CONTENTS.

xi

PAGE

the Shiri Highlands — Nature of the south Nyassa region — Changes in the geological character of this region in the latitude of Mount Waller — Extent of the Mount Waller sandstones — Relation of these deposits to the other African sediments — Later deposits above them — Drummond’s beds — -African lake pleistocenes — Arrangement of these different deposits — Extent of Drummond’s beds — Vast extent of the old African sandstones — Demonstration of the existence of a great depression in the region of the lakes before the formation of the Great Central Range — The broad features of the past history of these regions ............ 54

Chapter V

THE GEOLOGICAL TOPOGRAPHY OF THE REGION NORTH OF TANGANYIKA TO THE ALBERT NYANZA.

Want of knowledge of the districts north of Tanganyika — Importance of these districts in the consideration of the Tanganyika problem — Wide geographical effects produced by the recent formation of the Mfumbiro Mountains — Character of the country north of Tanganyika to Kivu — Former short extension of Tanganyika north — Absence of any former connection of Tanganyika with Kivu — Characters of the Rusisi channel — Characters of the Kivu basin — Peculiarity of the Kivu water — The north shore of Kivu and the Mfumbiro Mountains — The volcanoes form a dam across the lake valley — Character of these mountains — The valley of Kivu continued beyond them northwards —

The fauna of Lake Kivu is totally different from that of Tanganyika, but similar to that of the Albert Edward Nyanza — Former connection of Kivu and the Albert Edward — The volcanoes have resulted in the outflow of the Kivu being turned into Tanganyika and a corresponding shrinking of the waters of the Nile — The effect of this on the districts north of Kivu — The effect of this on the districts south of Kivu — Relation of the Mountains of the Moon to the Great Central Valley of the Lakes — Structural peculiarities of these mountains They are an accentuation of the folding characteristic of the region of the Great Central Range — Misapprehensions of Sir Harry Johnston ... 76

Chapter VI

AFRICAN PARK LANDS, THEIR APPEARANCE ON ALLUVIAL FLATS CONSIDERED AS EVIDENCE OF RECENT PHYSICAL CHANGE.

Characters of African Park lands — Artificial appearance of these districts — Their vast extent — Impermanance of Park scenery — A park is an artificial product — Relation of African parks to alluvial plains — Zoned character of the vegetation on freshly-formed alluvial plains — The relation of Euphorbias to bush patches — Gradual conversion of bush patches into forest — The production of an African park marks a phase in a gradual physical change . . . .107

TI1E TANGANYIKA PROBLEM.

xii

Chapter VII. General Outline Of The Zoology Of The Great African Lakes

The thirteen Great African Lakes, the fauna of which is more or less completely known — The lakes examined during the two Tanganyika expeditions — Other sources of information — The fauna of Lake Nyassa — Some physical characters of the Nyassa valley — Limitations of the Nyassa fauna— It is that of a great pond — The fauna of Lake Shirwa — Kela — Rukwa — Bangweolo — The fauna of Lake Mwero — The fauna of Lake Kivu — The fauna of the Albert and the Albert Edward Nyanzas — The fauna of the Victoria Nyanza — Nature of the Nyanza depression — The fauna of Lake Rudolf — The fauna of Lake Tanganika — Peculiarities of the fish fauna of Lake Tanganyika — The fauna of the great rivers of Central Africa — The distinctive elements of the fauna of Lake Tanganyika — Definition of the Halolimnic group . . . . . .120

Chapter VIII. On Some Curious Features Of The Distribution Of Species

General poorness of the African lake faunas — The faunas of the different lakes are specifically distinct — The faunas of these different lakes do not appear to intercolonize — The number of species in the Great African Lakes is directly proportional to their size — Unique climatic conditions affecting the Great African Lakes — Similarity of lacustrine faunas to island floras — On the causes which tend to the production of species characteristic of the different depressions . . . . . . . . . . . . .144

Chapter IX. The Fishes Of Lake Tanganyika

Descriptions of the eighty-seven species hitherto obtained

• 152

Chapter X. The Molluscs Of Lake Tanganyika

The normal and Halolimnic gastropods — Details of the structure of the Ilalo-

Chapter XI. The Affinities Of The Halolimnic Gastropods

Inter-relationships of the Halolimnic forms — Their primitive characters — They are not comparable to any existing fresh-water forms, but they structurally antecede a number of existing marine genera — The Halolimnic gastropods present the appearance of an old marine relic 266

CONTENTS.

xiii

Chapter XVI. General Consideration Of The Nature Of The Halolimnic

FAUNA.

Recapitulation of certain matters discussed in earlier pages — The geographical isolation of the Halolimnic group — Its coexistence with the normal African fresh-water fauna — The distinctive character of the Tanganyika fishes — The general characters of the components of the normal Tanganyika fauna — These are not structurally intermediate between those of the general African fresh-water fauna and the Halolimnic group — The Halolimnic gastropods cannot be regarded as derivitives from any recognised fresh-water types — Similar reasoning applies to the Tanganyika jelly-fish — Impossibility of regarding the marine characters of the Halolimnic group as having been brought about through convergence — Impossibility of regarding the Halolimnic group as the relic of an old fresh-water stock — The presence of the Halolimnic animals necessitates the supposition of a former extension of the sea into Central Africa, and thereby throws light into the geological history of the continent 325

XIV

THE TANGANYIKA PROBLEM.

Chapter XVII. General Consideration Of The Nature Of The Hal0limn1c

On some peculiarities of the fish-fauna in lake Tanganyika — Relation of some of the characteristic forms to both sides of the Atlantic — The character of the fishes of Tanganyika indicate that part of the fish fauna may have originated from a western sea — Peculiarities of the Congo fauna — The Congo depression probably the remains of a former extension of the sea — The age and type of the Halolimnic fauna — Comparison of the hard parts of the Halolimnic animals with fossiliferous remains — The identity between the shells of the Halolimnic gastropods and a corresponding number of forms from the Jurassic seas — Details of this comparison — General consideration of the value of this comparison— No valid geological objection to it — The number of corresponding points renders it improbable that the correspondence is a coincidence — The Halolimnic fauna would thus appear to be the remains of that of a Jurassic sea — The characters of the other Halolimnic animals in accord with this view — Recapitulation ■ 339

LIST OF ILLUSTRATIONS.

Head man of the Second Tanganyika Expeditions. — Frovi a Sketch

by the Author ........ Frontispiece

CHAPTER II.

PAGE

Lake Shirwa, looking west from the middle of the lake. — From a

Sketch by the Author . . . . . . . .22

View of the Zambesi and Shupanga, looking south-west. — From a

Sketch by the Author ...... F'acing 30

CHAPTER III.

View of Mount Morumbala, from the Shiri river. — From a Sketch by

the Author ........ Facing 34

View over the town of Ujiji and across Lake Tanganyika. — From a

Sketch by the Author . . . . . . . 37

View across the great central eurycolpic fold, from the northern

slopes of the Mfumbiro Mountains . . . . . 41

Diagrams of the geology of the Nyassa Valley . . . Facing 42

Diagrams of the Nyassa and Tanganyika Valleys . . Facing 44

The east coast of Nyassa . . 45

View of a portion of the Livingstone Range, from Nyassa . . 47

CHAPTER IV.

View over the alluvial flats at the north of Lake Nyassa. — From a

Sketch by the Author ...... Facing 56

View of one of the alluvial flats in the region of South Nyassa . . 59

View over the forests on the Nyassa Tanganyika plateau. — From a

Sketch by the Author ........ 63

XVI

LIST OF ILLUSTRATIONS.

PAGE

View from the top of the sandstone cliffs flanking the south-west

coast of Tanganyika. — From a Sketch by the Author . . . 67

View from the southern end of Lake Tanganyika. — From a Sketch by

the Author ........ Facing 68

CHAPTER V.

View of the south end of Lake Tanganyika, from Kituta. — From a

Sketch by the Author . . . . . . . .78

The great active cone of Kirungo cha Gongo. — From a Sketch by the

Diagram of Tanganyika and Kivu .....

View from the north end of Lake Kivu of the great active

Facing cone of

Kirungo cha Gongo .......

Bird’s-eye view of the Mfumbiro Mountains and the north

end of

Lake Kivu ........

View from the summit of Kirungo cha Gongo .

View of the steep west coast of the Albert Edward Nyanza View up the higher portion of the Mobuko Valley. — From

Sketch by the Author ........

The snow summit of Ngomwimbi .....

The northern snow ridge of Ngomwimbi

The broad glacier on the northern snow ridge of Ngomwimbi

io5

Diagram of the region north of the Albert Edward Nyanza

CHAPTER VI.

View of the snow peak of Kanyangogwi ....

Semi-diagram of the formation of Park-lands .

hi

CHAPTER IX.

Protopterus aethiopicus and Polypterus congicus

*54

Citharinus gibbosus .......

Barbus platyrhinus ........

Barbus altianalis ........

*59

Barbus tropidolepis ........

Capoeta tanganicae ........

Barilius tanganicae ........

1(3 5

Synouontis granulosus . . . . :

LIST OF ILLUSTRATIONS. xvii

PAGE

Cbrysichthys brachynema . . . . . . . .169

Lates microlepis . . . . . . . . . *171

Tilapia labiata . . . . . . . . . .173

Synodontis multipunctata ...... Facing 174

Paratilapia calliura, Ectodus longianalis and Tilapia boops . 175

Paratilapia furcifer . . . . . . . . . 177

Trematocara marginatum. . . . . . . . *179

Lamprolagus modestus and Haplochilus tanganicanus . . 181

Bathybates fasciatus . . . . . . . . -183

Bathybates ferox ........ Facitig 184

Judilochromis ornatus . . . . . . . . -185

Eretmodus cyanostictus, Telmatochromis vittatus and Lamprologus

Grammatotria lemairii . . . . . . . . .189

Paratilapia vittata and Xenotilapia sima ...... 191

Gephyrochromis moorei, Ectodus melanogenys and Tilapia grandoculis 1 93 Tilapia trematocephala, Paratilapia aurita and Paratilapia nigripinnis 195 Petrochromis polyodon . . . . . . . . -197

Lamprologus lemairii, Asprotilapia leptura and Lamprologus furcifer 199 Tilapia pleurotaenia ......... 200

Tilapia dardennii ........ Facing 200

Trematocara unimaculatum and Paratilapia leptosoma . . . 201

Lamprologus moorei ......... 203

Telmatochromis temporalis ........ 204

Tilapia microlipis and Tilapia rubropunctata . . . Facing 204

Lamprologus compressiceps, Paratilapia pfefferi and Ectodus longianilis 205 Paratilapia dwindti, Xenotilapia ornatipinnis and Barbus serrefer . 206

Tilapia microlepis and Barilius moorei ...... 208

Barilius moorei and Tropheus moorei ...... 209

Paratilapia stenosoma . . . . . . . . .211

Lamprologus elongatus, Mastacembelus taeniatus and Perissodus

Mastacembelus frenatus and Mastacembelus moorei . . . .215

CHAPTER X.

Melania admirabilis, Fig. 1 . . . . . . .219

Living Typhobia horei, Fig. 2. . . . . . . .221

Semi-diagram of anatomy of Typhobia horei, Fig. 3 . , . .222

B xviii LIST OF ILLUSTRATIONS.

PAGE

Lingual dentition of Typhobia horei, Fig. 4 . . . .223

Semi-diagram of anatomy of Typhobia horei , Fig. 5 . . . .224

Section of otocyst of Typhobia horei , Fig. 6 . . . .225

Part of the mantle cavity of Typhobia horei , Fig. 7 . . . .226

Bathanalia howesi shell, Fig. 8 . . . . . .227

Operculum of Bathanalia , Fig. 9 . . . . .227

Lingual teeth of Bathanalia, Fig. 10 . . . . . .228

Shell of Chytra kerkii, Fig. 1 1 . . . . . . .229

Living animal of Chytra , Fig. 12 . . . . . . 229

Nerves of apporrhais pes pelicani, Fig. 13. . . . . .230

Lingual teeth of Chytra, Fig. 14 . . . . . -231

Nerves of chytra, Fig. 15 ........ 232

Operculum of Chytra, Fig. 16. . . . . . . *233

Shell of Limnotrochus , Fig. 17 . . . . . . >233

Operculum of Limnotrochus, Fig. 18a . . . . . . 233

Lingual dentition of Limnotrochus , Fig. 18 . . . . 234

Nerves of Limnotrochus , Fig. 19 . . . . . . -"235

Stomach of Limnotrochus , Fig. 20 ...... 237

Shell of Bythoceras , Fig. 21 . . . . . . . 238

Lingual dentition of Bythoceras , Fig. 22 . . . , . . 239

Nerves of Bythoceras, Fig. 23 . . . . . . . . 240

Bythoceras minor shell, Fig. 24 ... 242

Lingual dentition of Paramelania damoni, Fig. 25 . . . . 243

Lingual dentition of Paramelania cranigranuluta, Fig. 26 . . 244

Shell of Paramelania damoni, Fig. 27 . . . . . 242

Shell of Tanganyicia rufofilosa. Fig. 2S . . . . . . 246

Semi-diagram of Tanganyicia rufofilosa, Fig. 29 . . -247

Lingual dentition of Tanganyicia rufofilosa. Fig. 30 . . . . 248

Nerves of Tanganyicia rufofilosa, Fig. 31 . . . . . 248

Semi-diagram of Tanganyicia rufofilosa , Fig. 32 ... 249

Shell of Nassopsis fiana, Fig. 33 . . . . . . .250

Semi-diagram of Nassopsis nana, Fig. 34 . . . . *. 25 1

Animal of Nassopsis, Fig. 35 . . . . . . . -252

Lingual dentition of Nassopsis nana, Fig. 36 . . . . . 253

Nervous system of Nassopsis, Fig. 37 . . . . . *254

Operculum of Nassopsis, Fig. 38 . . . . . 255

Shell of Spekia zonata, Fig. 39 . . . . . . .256

Lingual dentition of Spekia zonata, Fig. 40 . . . -257

LIST OF ILLUSTRATIONS. xix

PAGE

Nervous system of Spekia zonata, Fig. 41 ..... 258

Semi-diagram of Spekia, Fig. 42 . . . . . . .259

Semi-diagram of Spekia, Fig. ^3 ...... 260

Shells of Neothauma, Fig. 44 . . . . . . .261

Nervous system of Neothauma, Fig. 45 . . . . . . 263

Nervous system of Vivipara, Fig. 46 . . . . . .264

CHAPTER XL

Diagram of molluscs . . . . . . . . -273

Diagram of molluscs . . . . . . . . - 275

CHAPTER XII

Limnothelphusa maculata, Fig. 1 . . . . . .281

Platythelphusa armata. Fig. 2 . . . . . . .285

Limnocaridina tanganyikice, Fig. 3 . . . . . . .287

Palaemon moorei , Fig. 4. . . . . . . .293

CHAPTER XIII.

Arachnoidiae ray lankesteri ........ 296

CHAPTER XIV.

Living Tanganyika medusa ........ 299

„ „ „ , another 301

Semi-diagram of medusa buds ........ 303

Young bud 305

CHAPTER XV.

Spotigella moorei . . . . . . . . . .311

Skeleton of Spongella moorei . . . . . . . .313

Spongella tanganyikce . . . . . . . . .319

Potamolepis veltneri . . . . . . . . . 323

CHAPTER XVII.

Pyrgulifera humerosa . . . . . . . . 343

Paramelania and pur purina . . . . . . • 345

Nassopsis and purpurina. . . . . . . . *34 7

XX

LIST OF ILLUSTRATIONS.

PAGE

Amberleya and Bathanalia , 348 .

.

Limnotrochus and Jurassic shells .

.

Chytra and 0 nust us .......

.

35°

Spekia and Niridomus .......

.

Melania admirabilis .......

* *

MAPS.

Map of new positions on Lake Tanganyika

Map of the route of the Tanganyika Expeditions

Geological Map of the Nyassa region . . . .

Geological Map of the Tanganyika region

Map of the distribution of aqueous deposits in part of the African

Ft icing

Geological Map of the districts north of Tanganyika to