1907.] MEDUSiE FROM AFRICAN LAKES. 651 



LiMXOCNIDA TANGANIC^ * Var. VICTORIA. 



On comparing some shrunken and rather battered specimens 

 of Limnocnida obtained by Sir Charles Eliot, K.C.M.G., from the 

 Victoria ISTyanza, with the Tanganyika material, I considered 

 that I could detect diflerences in the specimens from the Victoria 

 Nyanza which may be regarded as sub-specific in importance : 

 the proximal ends of the older tentacles are more deeply sunk in 

 the jelly of the ex-umbrella than is the case in Limnocnida tan- 

 ganicce and the jelly-mass is more deeply grooved in consequence 

 (PI. XXXVII. figs. 4 & 5). 



About one third of the length of the older tentacles is smooth 

 and free from nematocyst warts, which are confined to the distal 

 two- thirds. The proximal ends of the tentacles which are adherent 

 to the exumbi'ella are specially supported by the development of 

 grooved lumps or ridges of jelly in which they lie. I have never 

 seen these so strongly developed in any Limnocnida from Lake 

 Tanganyika. The sense-organs were numerous, and very pro- 

 minent on the margin of the umbrella. 



The specimens examined were all females of about the same age, 

 with mature ova on the manubrium, and with tentacles of the 

 Vllth order. 



This collection was referred to by Prof. tSir Ray Lankester, at 

 a meeting of the Zoological Society on December 1st, 1903. The 

 meditsse were captured by Mr. Hobley at Kisumu on August 31, 

 1903, and had been preserved in a 5 ^o solution of formalin. 



The extremely interesting fact of the occurrence of a form 

 apparently identical with L. tanganicce in the delta of the river 

 Xiger about 102 geographical miles from the sea, proves that 

 Limnocnida must no longer be regarded as peculiar to the deep- 

 water lake Tanganyika, but that it has a wide distribution in the 

 fresh waters of tropical Africa. And as a consequence the 

 halolimnic theory, according to which Tanganyika is a jjersistent 

 Jurassic sea, in so far as it has been based upon the belief of 

 the exclusive occurrence of Limnocnida in that lake, falls to the 

 ground. 



With regard to the details of the change from a marine to a 

 fresh-water environment, we have yet much to learn from a more 

 searching study of Central African geology. Of all the theories 

 which have yet been proposed, we find ourselves most in agreement 

 with that outlined by Mr. Boulenger for the benefit of the 

 British Association in South Africa (1905), but the details of this 

 theory of a wide-spread Eocene Sea still require working out. 



More recently an oi'iginal speculation has been published by 

 Prof. Sollas. Of Limnocnida my imaginative friend writes (' Age 

 of the Earth," p. 209) — " If while in the hydroid stage, it grew 



* This would seem an appropriate occasion for advocating a more reasonable 

 uniformity in the spelling of this specific name ; and although in my original paper 

 1 had followed Bohm's spelling tanganyiccB in accordance with the laws of priority, 

 in the present communication the more usual and shorter form tanganicm is 

 adopted. I have noted tanganyicce, tanganicanus, tanganicensis, tanganyikce , 

 tanganyicensis, tanganika, and in Sollas's ' Age of Eai'th,' p. 209, tanganyicoea (!) 



