414 



NATURE 



[August 24, 1905 



sent in such a way that it is believed possible, at certain 

 seasons, for a man in a boat to pass from the one into 

 the other, points to the existence, until very recently, of a 

 more effective separation. Such problems are of the 

 greatest interest, and a more exact knowledge of the fishes 

 will help towards their solution. 



There is another aspect of the question of geographical 

 distribution which has assumed special importance of late, 

 especially in the writings of Prof. Osborn, Mr. Lydekker, 

 and Dr. Scharff, and of which Dr. A. E. Ortmann's paper 

 on the distribution of Decapod Crustaceans, published 

 three years ago, may be taken as an example. One of 

 the conclusions formulated therein is that " any division 

 of the earth's surface into zoo-geographical regions which 

 starts exclusively from the present distribution of animals 

 without considering its origin must be unsatisfactory." 

 But in certain groups of animals, possibly in most, the 

 question of their origin is not easily settled ; in the case 

 of the African fresh-water fishes, for instance, we sadly 

 lack all direct palseontological data, such as have sprung 

 up lately in marvellous profusion in the case of the 

 mammals, and notwithstanding the great progress in our 

 knowledge of the changes that have taken place in the 

 configuration of the world in Secondary and Tertiary 

 times, which has been conveyed to a wide circle of readers 

 chiefly through the luminous works of Neumayr, Suess, 

 and de Lapparent, there is still much that is open tso dis- 

 cussion. It must be admitted — and it is well to draw- 

 special attention to this point — that Dr. Ortmann's maps 

 of the land-areas in past periods, which render his sug- 

 gestive paper so attractive, cannot be accepted as the ex- 

 pression of well-established geological facts, and are, in 

 some respects, gravely misleading. If I have attempted 

 to deal with this subject on the lines laid down by Dr. 

 Ortmann, whilst realising the want of many necessary 

 data, palseontological and geological, on which to base 

 conclusions, it is with a due sense of humility, being fully 

 aware that the suggestions now offered must be regarded 

 as mere speculations. 



The time has come for a stock-taking of our immensely 

 increased material, the previous accounts of the distribu- 

 tion of African fishes given by Dambeck in 1879, by 

 Gunther and by Sauvage in 18S0, and by Palacky in 1S95, 

 no longer answering, even approximately, to our present 

 knowledge, as may be seen bv comparing the lists given 

 by these authors with the one I have quite recently pub- 

 lished in the Annals and Magazine of Natural History 

 as a basis for the sketch here attempted. 



How little we knew of the fresh-water fishes of Africa 

 when the subject was dealt with by the above-named 

 authors is exemplified by the enormous number of genera 

 and species which have been discovered within the last 

 few years, thanks chiefly to the enlightened activity of 

 the Governments of Egypt and the Congo Free State, and 

 to the initiative of Prof. Ray I.ankester in organising 

 explorations of the great lakes of Central Africa. The 

 waters of the French Congo and Cameroon, the Niger, 

 Abyssinia, and the interior of East Africa, have also 

 yielded a large number of novelties ; even the Nile, com- 

 paratively so well known, has been productive of 

 many and remarkable additions to our knowledge. The 

 importance of a better acquaintance with the fishes of the 

 Low«r Nile, a district believed to have been particularly 

 well explored, can be measured by comparing the present 

 data with those to which Prof. Gregory, on the faith of 

 Dr. Gunther 's list, appealed to justify his theory of a 

 direct connection in the past of the Upper Nile with the 

 Jordan through a river flowing along what is now the Red 

 Sea. To this question we shall revert presently. 



Whilst the exploration of rivers and lakes has resulted 

 in such a rich harvest, it remains a matter for serious 

 regret that we should still be without any information 

 as to the precursors of the African fishes. In spite of 

 diligent search over a considerable portion of the great 

 continent, no remains of any post-Triassic fishes have yet 

 been discovered in Tropical and .South Africa, and our 

 acquaintance with Tertiary Teleosts generally is still almost 

 as scanty and fi'agmentary as it was twenty years ago, 

 although mu:h has been done by Dr. Smith Woodward 

 in elucidating the afifinities of such remains as have been 

 exhumed. In the circumstances we have to fall back on 

 our imagination to explain the origin of the most important 



NO. 1869, VOL. 72] 



groups characteristic of the present African fish-fauna, and 

 much hazardous speculation has been indulged in. Thus, 

 without any sort of evidence, the Cichlid Perches of Africa 

 have been supposed to emanate from ancestors inhabiting 

 hypothetical Jurassic or Cretaceous seas extending over 

 Central Africa, whilst connecting land areas have been 

 too freely postulated to account for the resemblance between 

 the fishes of Africa and Tropical America, and antarctic 

 continents devised to explain the presence of Galaxias in 

 South Africa. To these suggestions I shall refer further 

 on when dealing with the distribution of the families to 

 which they were intended to apply. Although it is highly 

 desirable that zoologists should base their theories of geo- 

 graphical distribution upon geological data, I think we 

 must regret the growing tendency to appeal to former 

 extensions of land or sea without sufficient evidence, or 

 even contrary to evidence, in order to e.xplain away the 

 riddles that offer themselves. 



Twenty-five years ago a list of the African fresh-water 

 fishes would have included the names of about 350 species 

 (Gunther gave the number as 255 only), some fifty of 

 which have since lapsed into the synonymy, whilst at the 

 present day we are acquainted with 976 species, referable 

 to 185 genera and forty-three families. Of the latter five 

 were then unknown, or unknown to have representatives 

 in this part of the world. The forty-three families are 

 here enumerated, with an indication of the number of 

 genera and species according to the most recent census : — 



CHONDROPTERYGII. [ Haplomi. 



Pl.^giostomi. I 'S. GalaxiidEE, i, 2. 



19. Kneriidse, 1,2. 



13 



1. Carchariidse, i, i. 



2. Pristlda;, i, i. 



CROSSOPTERYGII. 



Cladistia. 



3. Polypteridae, 2, 11. 



DIPNEUSTI. 



4. Lepidosirenidae, i, 3. 



TELEOSTEI. 



Malacopterygii. 



5. Elopids, 2, 3. 



6. Mormyridae, 11, 108. 



7. NotopteridiE, 2, 2. 



8. Osteoglossidae, i, i. 



9. Pantodontidae, i, i. 



0. PhractolsemidcE, i, i. 



1. ClupeidiE, 6, 7. 



2. Salmonidas, i, i. 

 Cromeriidas, i, i. 



Ostariopiivsi. 



Characinidae, 20, 93. 

 Cyprinida 



20. CyprinodontidiE, 5, 



Catosteomi. 



21. Gastrosteidas, i, i. 



22. Syngnathidae, 2, 3. 



Percesoces. 



23. Scombresocidae, i, 



24. Atherinidae, 2, 3. 



25. Mugilidae, 2, 13. 



26. Polynemidae, 3, 3. 



27. Sphyraenidae, i, i. 



28. OphiocephalidiE, 1, 



29. Anabantidee, i, 14. 



ACANTHOPTERVGII. 



30. Centrarchidic, i, 3. 



31. Nandidae, i, i. 



32. Serranids, b, S. 



33. Sci^nids, i, i. 



34. Pristipomatidas, 2, : 



35. Sparida;, i, i. 



36. Scorpididae, i, 3. 



37. Osphromenida>, 1, 1 



38. Cichlida;, 30, 179. 



39. Pleuronectidic, 2^ 2. 



40. Gobiid*, 2, 31. 



41. Blenniidae, 3, 3. 

 Opisthomi. 



42. Mastacembelidae, i, 

 Plectognatiii. 



43. Tctrodontidae, i, 4. 



14. 



15- __ 



16. Silurids, 37, 187. 



.\PODES. 



17. Anguillidas, i, 6. 

 In discussing the distribution of the fresh-water fishes 



it is necessary to divide them into four principal cate- 

 gories : — 



(i) Those living part of the year in the sea. This cate- 

 gory is again subdivided into anadromous forms, breeding 

 in fresh water (ex. some Clupea), and catadromous forms, 

 breeding in salt water (ex. .\nguilla). 



(2) Those living normally in the sea, but of which certain 

 colonies have become land-locked, or have separated them- 

 selves from the marine stock still represented on the 

 neighbouring coast (ex. some Gobiidje and Blenniidae). 



(3) Those which, although entirely confined to fresh 

 waters, have as nearest allies species living in the sea, 

 and which there is reason to regard as more or less recently 

 derived from marine forms (ex. Galaxiid^, Tetrodontidie). 



(4) Those belonging to families entirely (ex. Mormyrid*, 

 Characinida^) or chiefly (ex. Silurids, Cyprinodontidae) 

 restricted to fresh waters. 



