1918.] Mollusca Pulmonata. 459 
the others, while the lateral teeth gradually change into mar- 
ginals from within outwards. There are about eight rows that 
can be called lateral and six that are definitely marginal. All 
the teeth are extremely minute; in general form they may be 
described as being intermediate between those of Planorbis and 
those of Ancylus. Their cusps are stout and their denticula- 
prominent than either of the lateral projections; the whole 
structure is asymmetrical and there is a shallow sloping super- 
ficial groove separating the right denticulation from the cen- 
tral one. The cusps of the lateral teeth are very similar, except 
that the innermost denticulation is the largest. This becomes 
more accentuated as the marginal region of the radula is ap- 
proached. The innermost denticulation is occasionally divided. 
The cusps of the marginals are almost pectinate and form a 
sloping ridge in which the innermost part is the most promi- 
nent. ; 
We can find no trace of a horny jaw. 
_ _ Habits.—So far as habits are concerned the Japanese form 
is identical with Benson’s. He and his friend Dr. Bacon found 
condition. The curious almost membranous rim of the aper- 
ee a etree 
’ 
p. 185 (1906). 
| Lankester’s Treatise on Zoology, Mollusca 
