belonging to the shell, is a point on which I am unable to give a de- 
cided opinion : the determination must, therefore, be left to those who 
may have better opportunities of pursuing the inquiry. 
A specimen is figured by Baier, resembling T. lata in form, but 
which is much smaller, and appears to be marked externally with trans- 
verse striae. Whether this is only a young one of the species T. lata , 
is difficult to say ; but in one of my specimens, is an impression of the 
two opened valves of a small shell, in which I observe an exact agree- 
ment with the proportions of the valves of that species. In this speci- 
men I also observe traces of the impressions of a similar appendicular 
substance with that already noticed. 
CXY. Venus. An equivalved, rather inequilateral bivalve, with 
three hinge teeth in each valve, converging at their base towards the 
beaks. The middle tooth, which is sometimes bifid, is placed straight, 
and the one on each side obliquely. 
Lamarck particularizes six fossil species, which are found in the neigh- 
bourhood of Paris : V. mutabilis, V. obliqua , V, callosa, V. texta, V. 
scobinellata, V. puellata. Of the first of these, V. mutabilis, he ob- 
serves, that it is the most singular shell which he knows, with respect 
to the variety which it exhibits in its hinge. It is a roundish, elliptical, 
transverse, compressed shell, bearing only very fine striae on its surface, 
the marks of its increase ; the hinge, in old shells, without teeth. In the 
young specimens, the three teeth, characteristic of the genus, are gene- 
rally observable ; but, even among these, one or two of the teeth are 
sometimes effaced. On viewing the older specimens, the teeth are so 
frequently absent, that it might be supposed, that none belonged to 
the species. On the inside of the valves are very fine serrated and 
radiating striaB ; but which, not reaching to the edge, leave it smooth. 
Among the admirable silicized shells of Devonshire is found a fossil, 
which appears to be undoubtedly referable to Venus castrensis. In a 
specimen with which I was favoured by Mr. Clarke, the shell is per- 
