UNIVALVES. 63 
family, to which they belong, contains the peri- 
winkles and numerous other marine snails. The 
family may be distinguished from the preceding 
ones by the shell being spiral and conical, the 
operculum spiral, and the eyes sessile at the 
outer bases of the tentacles. 
The genus Assrurnta (from the Latin assimilis, 
very like) is represented by one British species, 
Assiminia Grayana (PL. II., fig. 8), imhabiting 
the banks of the river Thames between Green- 
wich and Gravesend, living on the mud beneath 
the shade afforded by Scirpus maritimus, Festuca 
arundinacea, &c. It is very abundant. 
The animal of <Assiminia differs from the 
marine Fissoa, in the tentacles bemg united to 
the eye-stalks, which equal them in length. The 
shell of A. Grayana is ovate, acute, solid, 
shining, of a liver-brown colour, and is about 
Fig. 10.—Teeth of A. Grayana (Lovén). 
a quarter of an inch in length; the whorls are 
five in number; the suture is slightly im- 
pressed ; there is no umbilicus; the aperture is 
ovate ; the operculum is horny, ovate, and of a 
