187 



on which I am unable to give a decided 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 transverse 

 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. 



CXV. 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. scobi- 

 nellata, V. pudlata. Of the first of these, V. mutabilis, he observes, 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 generally 

 observable ; but, even among these, one or two of the teeth are some- 

 times effaced. On viewing the older specimens, the teeth are so fre- 

 quently absent, that it might be supposed, that none belonged to the 

 species. On the inside of the valves are very fine serrated and radiat- 

 ing striae ; 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 spe- 

 cimen with which I was favoured by Mr. Clarke, the shell is perfectly 



