marine British Shells and Animals! ^ > 191 
difference in the formation of these shells must occasion a very 
material dissimilarity in the situation and structure of the teeth, 
as well as in the conformation of the animals tbat inhabit them. 
What those fossil shells really may be, or to what genus in con- 
chology they might be referred, which are destitute of any per- 
foration, and which have been placed amongst the Anomie, is not 
to be determined, since the structure of the teeth is concealed 
from our view, as the greater part of them are complete petrifac- 
tions, and have their valves closed. We may, however, be as- 
sured that the animal which inhabited such imperforate shells, 
must have been very different from those which are known to 
inhabit such as are perforated. : 
"The Mya inequivalvis of Testacea Britannica is in the fossil 
state considered as an Anomia, though it has strictly the hinge of 
a Mya, and the animal inhabitant is materially different from 
what is observed in either of the perforated recent Anomia. | 
— But let us go further, and examine the structure of some of the 
recent shells together with their animals, and I doubt not that 
most Conchologists will agree with me, that there is a much greater 
natural division between those which have the under valve per- 
forated, and such as have a perforation in the beak of the upper 
valve, than there is between a Tellen and a Venus, or indeed be- 
tween any two genera of the Linnzan system. We have only to 
look to the natural habits of these two kinds of shells, including 
their animal inhabitants; and if those, together with the external 
appearance, be not sufficient, let us have recourse to the internal 
structure, and especially the great leading characters, the hinge 
and teeth, and we shall find that the more strictly and accurately 
the comparison is made, the further will these shells appear to be 
separated from each other. If, for instance, the Anomia Ephip- 
pium be examined, it will be found that the animal is totally 
destitute 
