THE GASTROPODS CHYTRA AND LIMNOTROCHUS. 437 
(Pl. 40. fig. 28) are generally similar to those of Chytra Kirki *, 
except that in Aporrhais the supra- and sub-intestinal cords are 
considerably elongated, and there is a direct zygoneurous 
connection on the right side. In Chytra Kirkii there is, however, 
also a practically zygoneurous condition, the connecting nerve, 
instead of joining the sub-intestinal ganglion (PI. 39. fig. 14), joins 
the pallial nerve immediately after its origin. Lastly, the whole 
stomachic apparatus is similar: there is a_ well-developed 
erystalline style in Aporrhais (st., Pl. 40. fig. 22), and the internal 
valvular portion of the spiral cecum is present, but not the 
complete structure. Further, the barrel-shaped otoliths which are 
found in Chytra are also found in Typhobia (6. p. 188) and in 
the Cerithiide. The presence of the slightly developed spiral 
eexeum in Chytra brings this interesting form into relationship 
with Trochus (7. & Pl. 40. fig. 27), Plewrotomaria (fig. 28), and 
Nassopsis (5. p. 189, & Pl. 40. fig. 26). The presence of a crystal- 
line style characteristic of Chytra is characteristic of widely 
different molluscan forms. It is present in all the halolimnic 
Gastropods of Tanganyika, in some Trochide, Pteroceras, and 
the Strombide. These facts suggest that in Chytra we are 
probably dealing with the direct ancestor of the families 
Hipponycide and Capulide, since the genus combines the nervous 
system of the one and the radula of the other; 2.e¢., two of the 
most salient features of Prosobranchiate anatomy. 
Limnorrocuus THomsonr. (PI. 38. figs. 1-9; Pl. 40. fig. 24.) 
Limnotrochus Thomsont is now the single species of the 
genus (1). Like Chytra, it is an inhabitant of Lake Tanganyika, 
living at considerable depths and apparently in solitude, for 
never more than a single specimen is dredged at a time. Con- 
sequently it is difficult to procure the living animal, but the 
empty shells are pretty common. The conchological characters 
(Pl. 38. figs. 1, 2) presented by the genus, however, need no 
comment here, as they have already been fully described and 
figured (8. p. 285). The operculum (PI. 38. fig. 3) is “ horny ” 
and somewhat oblong in shape, concave towards the inner side, 
and Littorinoid in character. 
* Haller’s figure (3. taf. xvili. fig. 6) of the nervous system of Chenopus 
(Aporrhais) pes-pelecani and his description of the same (p. 579) is absolutely 
incorrect. He must either have ficured an entirely different animal, or the 
specimen that he dissected was quite abnormal, 
