MOLLUSCA. 113 
of this genus, the /acustris and fluviatilis, natives of Bri- 
tain. 
The genus PATELLA, as circumscribed by Lamark, has 
been already sufficiently noticed. The common limpit may 
serve as the type of this genus. 
In the genus FissurELwA, established by Bruguiére, 
there is always an opening like a key-hole, near the summit 
of the shell. The /. greca and apertura are found on our 
coasts. 
The genus EMARGINULA is readily distinguished by the 
slit or indentation which occurs on the posterior margin of 
the shell. 
In the genus Carutus of Montfort, the shell is conical, 
with the summit produced into a beak, more or less recurv- 
ed, and twisted. The P. hungarica of Lister is the type. 
« The genus ConcnHo eras is furnished with an opercu- 
lum, and in form and habits approaches the buccinum. It 
is represented by the P. zxtegra of Da Costa’s El. tab. 2. 
fig. 7. 
In the genus CrepipuLa, the cavity of the shell is par- 
tially interrupted by a simple diaphragm. The P. porcel- 
lana is the representative of this genus. The C. chinen- 
sis inhabits the British seas. 
In the preceding genus, the first approach to the turbi- 
nated shell makes its appearance, which becomes more ob- 
vious in the genus CaLypTrma, in which the cavity is fur- 
nished with a spiral diaphragm. The C. equestris is the 
type of the genus, which is related in part to the trochi. 
From this genus of Lamark, Montfort has separated the In- 
FUNDIBULUM, as possessing a central spiral pillar. Sow- 
erby has figured several species of this last genus in his 
