THE TANGANYIKA PROBLEM. 
33 1 
The jelly-fish in Tanganyika, as Mr. Gunther and I 
have shown, is possessed of a remarkable primitive type 
ol structure even among these forms. 
The sponges which are peculiar to Tanganyika, Spon- 
gilla tanganyikae and A. moorei , might be regarded as 
having originated from fresh-water types, but they could, 
except for their fresh- water habitat, as Mr. Evans pointed 
out, be just as well associated with the Chalinidae, a 
marine family group, and like the prawns they are not 
found outside the confines of the lake. Potamolepis , a 
sponge common to Tanganyika and the Congo, is a highly 
peculiar form, and the chief fact of importance, regarding 
it in this connection, is that its spicules are identical 
with those of the old fossil o-enus Renieria which occurs 
o 
extensively in the marine deposits of the secondary rocks. 
It is precisely the same with the Protozoa of Tanganyika, 
i.e., the remarkable Collpodium and Condylostoma peculiar 
to that lake. 
In considering the meaning of the peculiarities which 
characterise the constituents of the halolimnic group, 
it is a fact of very great importance that the normal 
fresh-water components of the fauna of Tanganyika are in 
no way peculiar ; they do not in the least stand as structural 
stepping-stones between the components of the general 
African fresh-water fauna and the members of the halo- 
limnic group. This point has been referred to again and 
again while dealing with the anatomy of the different 
organisms which constitute the halolimnic group. Hardly 
any of these halolimnic types could, in fact, under any cir- 
cumstances be regarded as modifications or specialisations 
of any of the recognised African fresh-water types. The 
halolimnic gastropods are quite incapable of being re 
garded as derivatives from the recognised fresh-water 
