Mollusca of the Tai-Hu. * 311 
whorls increase gradually and regularly. It is clothed with a polished epidermis of a 
deep chocolate-brown colour, which in the natural state is covered by an earthy depo- 
sit. Only three complete whorls remain in the specimens, but if they were not eroded 
at least five would be present. On the body-whorl there are three blunt continuous 
spiral ridges the lowest of which, lying very near the middle ridge, is almost obsoles- 
cent. On the other whorls there are two well-developed ridges. The surface is fur- 
ther ornamented with numerous coarse oblique longitudinal striae set close together. 
The aperture is ovate, pointed and a little folded anteriorly ; its inner margin is promi- 
nent and thickened but not very much flattened. The shell is narrowly umbilicate. 
The inner surface is greyish blue and highly pohshed. 
Fig. 5. — Radular teeth of Pseudovivipara hypocrites, sp. nov. 
Measurements (in millimetres) of three shells. 
Type. 
Length of shell . . 
• 17-5 
14-5 
14 
Greatest breadth of shell . 
10-6 
10 
9-5 
Length of aperture 
• 8-5 . 
7-3 
7-5 
Breadth of aperture 
. 6 
5 
5 
Length of operculum 
. 8 
Breadth of operculum 
• 5-6 
The operculum is large and thick, pyriform, almost bilaterally symmetrical, of an 
opaque white colour and porcelainous in texture but covered externally with a coarse 
chestnut epidermis, which is somewhat eroded in the central region. This region is 
deeply concave ; the external sculpturing is obscure, but concentric striae can be de- 
tected on the epidermis. The convex part of the inner surface is smooth except for 
obscure vermicular ridges of indefinite arrangement. 
In most respects the soft parts resemble externally those of Bithynia. Both the 
tentacles and the snout are relatively stout and broad ; the former are somewhat 
flattened but tapering, the latter is blunt at the tip and only very slightly emarginate. 
The foot is ovoid in shape, pointed but not produced posteriorly and slightly emargin- 
