VALVATID^. 
33 
species was ^^not characterised:” overlooking the 
fact that I pointed out the very marked difference 
between them found in the young shell ; thus firmly 
establishing the distinction which some concholo- 
gists had only considered as a sexual peculiarity, 
the most ventricose being the female. 
Fam. 5. VALVATID^. 
Rostrum annulated, elongate, bifid. Tentacles equal, 
elongate, tapering, rather blunt ; eyes on a 
small tubercle on the inner side of their base. 
Jaws, two, lateral, narrow, approaching each 
other above, where there is a third rudimentary 
jaw, like a small tubercle. {Moquin^ 32. t. 
41. f. 6.) Mantle-edge thin, with a tentacle-like 
appendix on the right side, which has been 
called the branchial thread. Vent on the right 
side, under the mantle. Gills plumose, exserted 
when the animal is expanded, formed of an 
oblong, tapering, conical process, furnished bn 
each side with a series of spirally- twisted laminge, 
placed opposite to each other, (f. 9. i.) Foot 
truncated, nicked slightly, and produced at each 
angle in front, rounded behind. The male 
organ is like a third tentacle, situated behind 
the base of the right tentacle ; the orifice of 
the female organ is under the collar on the 
right side of the vent. {ISIoquin^ t. 41. f. 5.) 
Hermaphrodite ; ” oviparous ; eggs emitted 
singly ; fluviatile, eating aquatic plants ; rarely 
