The Tanganyika problem; an account of the researches undertaken concerning the existence of marine animals in Central Africa . nects up two fairly ancient marine groups,for it possesses the characters of Capulus and its allies, andalso those of the Xenophoridse themselves. In LimnotrocJius we have, as I have pointed out, an allyof CJiytra, and the same inferences may be drawn from itsstructure. Turning now to the group of gastropods composed bythe genera Paramelania and BytJioceras and their subordi-nate species, we find that all these forms, both in theirradulae and nerves, present us with fe
The Tanganyika problem; an account of the researches undertaken concerning the existence of marine animals in Central Africa . nects up two fairly ancient marine groups,for it possesses the characters of Capulus and its allies, andalso those of the Xenophoridse themselves. In LimnotrocJius we have, as I have pointed out, an allyof CJiytra, and the same inferences may be drawn from itsstructure. Turning now to the group of gastropods composed bythe genera Paramelania and BytJioceras and their subordi-nate species, we find that all these forms, both in theirradulae and nerves, present us with features which are dis-tinctly similar to those of CeritJiium; but they are at oncedissociated from the Cerithoid group of Prosobranchs, bythe peculiarities of their gastric apparatus and their posses- * It has since been found in a reduced condition in Turritella communis. See paperby W. B. Randies, Anat. Anz. 1902 ; Bd. xxi., p. 201. THE TANGANYIKA PROBLEM. 273 sion of crystalline styles. They are probably correctlyregarded as a group of rather primitive Cerithoids, whichanteceded both the Amanda type of Melanias and the. Aplysia Auricula Actoeon Diagram to show the modifications witnessed in the reproductive apparatus in a numberof divergent gasteropods. , Genital gland. , Vas differens. , V, Genital groove. , Enclosed portion of vas differens. , Brood , Penis. , Hermaphrodite gland. , Hermaphrodite duct. , Seminalvesicle, , Evertable penis. modern Ceriths, which are found now inhabiting the seas. Tanganyicia is much more difficult to place ; it possesses 18 274 THE TANGANYIKA PROBLEM. the Cerithoid nervous system and a feebly developedradula, the teeth of which might with equal proprietybe regarded as approaching several diverse forms. Inthis group the most remarkable feature which is exhibitedconsists in the genital groove, which here leads into abrood pouch in the foot, on the left side of the head,a condition of things which may
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