DWIGHT VV. /AY LOR 
THE TANGANYIKA PROBLEM. 271 
and also of a number of divergent forms, such as Natica, 
Capulus, Conceliaria and Strut hiolaria. In minor details 
the nervous system of the Ty phobia group approaches more 
closely to that of Capulus and Cancellaria than it does to 
that of either Cerithium or M. amarula , while in the 
curious features of their gastric apparatus all the members 
of the Typhobia group are really closely approximated to 
such forms as Strombus and Pteroceras and Aporrhais. 
The members of the Typhobia group thus present a 
type of organisation which appears to stand at the parting 
of the ancestral ways of such widely divergent marine 
groups as those characterised by the following genera : 
Strombus , Pteroceras , Cerithium , Strut hiolaria, Cancellaria , 
Aporrhais and Capulus ; for each of these diverse, marine, 
modern gastropods contain, underlying their own peculiar 
specialisation, more or fewer of the characters which are 
compounded in the members of the Typhobia group. 
A similar and still more interesting result is obtained 
from the comparative study of the two genera Chytra and 
Limnotrochus. The whole anatomy of Chytra is singularly 
like that of Capulus. We have in both forms the same 
arrangements of the nerves, the pallial connectives being 
identical in both genera. So also the radula of Chytra is 
curiously like that of Capulus , and it corresponds even in 
minor details with the ally of Chytra , Hippnyx. Chytra , 
however, differs from both these genera, and all their 
more remote naticoid allies in the possession of a style 
sac. And what is even more remarkable, in the reten- 
tion in its stomach of a well-developed spiral caecum, 
a structure which, so far as I know, is only present 
in Nassopsis elsewhere among the Taenioglossa, but 
which, as is well known, is a characteristic feature of 
the stomachs of the more primitive Rhipidoglossa, such 
