434 MISS LETTICE DIGBY ON THE STRUCTURE OF 
On the Structure and Affinities of the Tanganyika Gastropods 
Ohytra and Limnotrochus. By Lerrice Dresy. (From 
the Biological Laboratory, Royal College of Science.) 
(Communicated by Prof. G. B. Howss, F.R.S., Sec. Linn. 
Soc.) 
[Read 20th February, 1902. ] 
(PLates 38-40.) 
Turs paper is based on material which formed part of the 
collection brought by Mr. J. E.S. Moore from Lake Tanganyika. 
He has kindly placed at my disposal specimens of both Chytra 
Kirkii and Limnotrochus Thomsoni, and has greatly helped me 
in my work. 
CHYTRA. 
The genus Chytra was separated by Moore from Smith’s 
original Limnotrochus (4. p. 307), the older generic name. being 
reserved for the reception of the single species Limnotrochus 
Thomsoni. The genus is now represented by a single species, 
Ohytra Kirkii (=L. Kirkii, Sm.), and is one of the most 
characteristic forms among the group of peculiar operculate 
molluscs found only in Lake Tanganyika. It has been generally 
placed among the Hydrobiide (ef Fischer 2.), a family often 
used as a receptacle for curious and abnormal types which have 
not been satisfactorily classed. But in 1897, Moore (4. p. 807) 
regarded it as more probably belonging to the Xenophoridex, on 
account of its conchological similarity to numerous fossils which 
are referred to that group. Up to the present time, however, 
the anatomy of the animal has never been described. 
External Features.—The shell (Pl. 38. figs. 1 & 2) has already 
been described by Smith (8. p. 286). The horny operculum (fig. 3) 
is of the Littorinoid type, the inner surface being convex and 
the outer concave. The tentacles are long and filiform, and the 
eyes are situated on tubercles at their bases. 
Nervous System.—The nervous system seems to be transitional 
between the dialyneurous and the zygoneurous types (Pl. 39. 
fig. 14). The cerebral ganglia (g.c.) are closely approximated, 
and the pleural ganglia (g.p.) are separated from them by a 
