THE GASTROPODS CHYTRA AND LIMNOTROCHUS. 439 
buccal cavity. The cesophagus is straight, except for a sharp 
bend before it opens into the stomach (PI. 40. fig. 24), which, 
like that of Chytra, has two chambers, the anterior of which 
contains a large crystalline style. The walls of the posterior 
chamber are very thin; those of the anterior chamber very thick 
and muscular. The most remarkable feature about the gastric 
apparatus of Limnotrochus lies, however, in the fact that it 
possesses an even better developed spiral cecum (ce., Pl. 40. 
tig. 24) than Chytra (fig. 25) itself. The base of the cecum is 
connected with a longitudinal fold which extends to the anterior 
chamber; the aperture of a bile-duct (d.) lies below the spiral 
cecum. The coils of the intestine, the rectum, and the anus 
are very similar to those of Ohytra. The kidney is fairly large, 
aud occupies the same position as in Chyéra, surrounding the 
‘“‘monotocardian ”’ heart. 
The gill (g., Pl. 38. fig. 9) is short, the gill-plumes are 
triangular, and the osphradium (o.) is filiform. 
In both specimens which I dissected, the long slit-like aperture 
of the genital gland (PI. 38. fig. 9, a.g.) opened into a considerably 
dilated sac, slightly curved towards tie left side of the animal. 
In the case of one specimen this was undoubtedly the uterus, as 
it contained bundles of very long spermatozoa ; and in the genital 
tissue of the visceral coil there were well-developed ova. 
There is a large accessory gland-like organ (fig. 9, g.g.') like that 
of Chytra, which spreads posteriorly into a tongue-shaped body, 
partly underlying the uterus (cf fig. 8). 
Affinities.—It will have been gathered from the preceding 
description that Limnotrochus Thomsoni, in the general plan of 
its organization, and in the disposition of the viscera, is distinctly 
like the genus Chytra, but in minor details very different. 
The shell of Limnotrochus Thomsoni (Pl. 38. figs. 1, 2) may bé 
compared to some of the so-called Littorinas of the marine 
Jurassic deposits, and in particular to Littorina sulcata (4. p. 317). 
It is also dissimilar to that of Cancellaria. 
Curiously enough, the nervous system of Limnotrochus 
(Pl. 38. fig. 5) is also like that of Voluta (3) and Cancel- 
laria, there being the same condensation of the cerebral, pleural, 
and pedal ganglia, and the same zygoneurous condition of the 
right side. The radula (Pl. 38. fig. 4) cannot be associated 
with any known type, its nearest approach is to be found in 
the varieties of the Melanoid group (9. vol. i. p. 121). 
