. 
. 
| 
| 
1918.] Mollusca Pulmonata. 461 
spire is short, flattened and lateral in position, the body-whorl 
large, ovoid, convex above and flattened on the ventral sur- 
face. The aperture, though little expanded, is relatively of 
great size, oval, with its main axis practically at right angles 
to that of the spire. The columellar fold is broad, flattened 
and turned slightly inwards, running obliquely across the pos- 
terior margin of the aperture and almost forming a septum in 
the posterior part of the shell. 
The soft parts apparently resemble those of Limnaea, ex- 
cept that the tentacles are long and cylindrical or subcylindri- 
cal; the mantle is incapable of being expanded over the shell 
and is not thickened or highly vascular at its lower margin. 
The upper jaw and radula exactly resemble those of Lim- 
ea. 
8 8-DABUG 
Fic. 2.—Radular teeth of Omia japonica (Preston). a= central 
tooth. b=lateral teeth. c = marginal teeth. 
_ _Type-species. Lithotis japonica, Preston, from Lake Biwa 
in Japan. 
orientation of its spire. In some respects the shell resembles 
figure some of the radular teeth and also the: upper 
e 
_jaw of the type-specimen of the type-species. The jaw is very 
\, 3). As Preston's figures (op. cit., pl. ix, figs. 6, 64) are not 
a correct, we have had fresh drawings made from the type- 
eu. 
_ Like Camptoceras, Omia has apparently a discontinuous 
jistribution. Not only is the animal extremely inconspicuous, 
Owever, but it is particularly liable to be overlooked on 
