OCR Text |
Show 1899.] CRUSTACEANS FROM LAKE TANGANYIKA. 711 pl. vii. f. 2) and Klunzinger (Zeitschr. f. wiss. Zool. xvi. 1866, p. 357, pl. xx.), appears to present distinctive characters. Both these authors figure the rostrum with a very convex upper edge. Klunzinger gives the number of serrations as ff^, Boux figures j # According to the figures of both authors, however, not more than one tooth appears to be behind the orbit. Both show the carpus of the 2nd peraeopod to be distinctly shorter than the merus, and much more than half the length of the hand. Klunz-inger's figure of the chela shows it to be more slender, with the palm less inflated and the fingers longer than in our species. Neither of the species described in this paper can be depended on as throwing any light on the general question of the origin of the Tanganyika fauna. The genus Palcemon contains about 50 species, of which only two are said to be marine. It is closely allied to Leander, in which, conversely, the marine species greatly predominate, while both genera have numerous allies among the littoral fauna. Whatever bearing the genus Palcemon may have on the more general problem of the origin of freshwater faunas, the number of its species, their wide distribution, and lastly the imperfect nature of the specimens from which the present species is described (precluding any conclusion as to its nearest specific affinities) all render it incapable of serving us towards the settlement of the special problem of Tanganyika. Limnocaridina belongs to the Atyidce, a circumtropical family of freshwater forms whose probably somewhat distant allies are supposed by Ortmann to be found in the deep-sea Acanthephyridce. It is a near ally of Caridina, an extensive genus, of which one species is known from the West Indies, while the rest occupy countries bordering on the Indian Ocean from S. Africa to Australia ; one species occurs in the Nile and the rivers of Algeria. One species, C. wyckii, has a range extending from East Africa to Queensland and Celebes. It is noteworthy from the point of view of the present case that Caridina is not known to occur in West Africa. Our form from Tanganyika is in the meantime an isolated species, and the characters that it presents are not those of a primitive type, but rather of a somewhat specialized form. EXPLANATION OF THE PLATES. PLATE XXXIX. Fig. 1. Limnocaridina fanyanyikw, g. et. sp. n., £, P- 704. 2. „ ,, Carapace and rostrum. 3. Caridina wyckii (Hickson), p. 705. Anterior part of carapace. 4. Limnocaridina tanganyikes, p. 704. Peduncle of antennule. 5. „ „ Mandibles. (5. „ ,, First maxilla. 7. ,, ,, Second maxilla. g. ,, ,, First maxilliped. 9. ,, Third maxilliped. 9 a. Terminal joint of third maxilliped. 46* |