276 DIMYARIA.—VENERIDZ. 
shell, and to the epidermis at the margin, and 
appears to be kept distended, and in contact with 
the interior of the valves, by the included water. 
The valves fit so closely that the animal can re- 
main two days or more without permitting a single 
drop of fluid to escape. Locomotion very con- 
fined; it is capable, with the assistance of its foot, 
which it used in the same manner (but in a much 
more limited degree) as the Cardiacea, of fixing 
itself firmly in the sand, generally choosing to 
have the wmbones covered by it, and the orifices of 
the tubes of the mantle nearly perpendicular. 
‘‘ Resting in this position on the margin of a sand- 
bank, of which the surrounding soil is mud, at too 
great a depth to be disturbed by storms, the 
Isocardia of our Irish sea patiently collects its food 
from the surrounding element, assisted in its choice 
by the current it is capable of creating by the 
alternate opening and closing of its valves.” * 
This fine species is nowhere very common; it 
is, however, occasionally taken in deep water off 
the extreme north of Scotland, and the extreme 
south-west of England, but it appears to be most 
abundant in the neighbourhood of Dublin. The 
other species are but few, and are found in the 
East Indian seas, and on the coasts of Australia. 
They inhabit mud and sand, at a depth ranging 
from ten to twenty fathoms. 
FAMILY VENERIDZ. 
(Venus Shells.) 
The best character of this extensive family is, ac- 
cording to Cuvier, that the teeth and lamin of the 
* Zool. Journ. ii. 359. 
