96 PHYTOPHAGA. 



Fam. 4. VALVATID.3E. 



The tentacles are elongate, tapering, rather blunt, 

 with the eyes on small tubercles at the outer 

 hinder side of their base; mouth rather pro- 

 boscidiform; the foot truncated and slightly 

 lobed in front, rounded and slightly nicked be- 

 hind; the gills are exserted when the animal 

 is expanded, and are formed of an elongate, 

 tapering, conical process, furnished on each 

 side with a series of spirally-twisted laminae, 

 placed opposite to each other, (p. 78. f. 13.) On 

 the hinder part of the right side, near the suture 

 of the whorls, is an exserted filiform member 

 (p. 78. f. 12.) like a tentacle, but rather shorter 

 and thicker, which is called the branchial thread 

 by Lamarck. 

 The shell conical, thin, covered with an olive peri- 

 ostraca ; the mouth round, with a continued peri- 

 stome. 

 The operculum is horny, suborbicular, formed of 

 many gradually enlarging whorls, which have a 

 raised membranaceous outer edge, forming a 

 spiral ridge on the outer surface, (p. 78. f. 14.) 

 The shells are known from Paludinae by the shelly 

 cone being circular, and not bent in in any part by 

 the proximate whorls. They are like the marine 

 genus Skenia of Fleming, which, however, has a dif- 

 ferent animal, very like that of Rissoa and Hydrobia. 



