Pvn H,i I'UitlS

VEXERID^. 325
and it even requires some degree of conchological faith
to believe in their existence. The present family abounds
in species mostly frequenting southern latitudes. Nearly
all of them live in soft ground, buried a couple of
inches in gravel, sand, or mud, or among nullipores.
A variety of Tapes pullastra, however, inhabits the de-
serted holes of Pholades and Saxicavce,
as well as the
crevices of submarine rocks, wisely accommodating itself
to the circumstances in which it happens to be placed.
Their bathymetrical range is very extensive, one kind
{Venus gallina) inhabiting the shore and the greatest
depth ever reached by the dredge. From the investi-
gations of Dr. Carpenter into the microscopical texture
of their shells, we learn that they are porcellanous and
hard, containing scarcely any animal matter. Some
kinds are supposed to occur in secondary formations ;
but owing to the main feature by which they are known
from other bivalves of the same shape being internal,
and therefore difficult to ascertain in petrifactions, their
geological history is necessarily
involved in some ob-
scuritv. Their own svstematic relations and divisions
into genera are also unsatisfactory. With the exception
of Lucinopsis, it is difficult to define any of these
genera by precise characters. Deshayes appears to
be right in rejecting the claims of Cytherea, and Clark
has given equally valid reasons for contesting the separation
of Artemis from Venus. I am not convinced
that Tapes has a better right to be considered distinct,
unless restricted to two out of the four British species
which have been assigned to that genus; but I will
retain it provisionally, in deference to other conch olo-
gi'sts. The number of genera into which it has been
proposed during the past century to distribute the spe-
cies of Venus alone, is almost incredible.