TO GEOLOGY. A 87 
having a smaller hinge. One of the fractured pieces 
seems to have a wider hinge, and may prove to be of a 
different species. 
About seventeen species have been found fossil in 
Great Britain. The lowest stratum being that of the 
Magnesian Limestone (Zechstein)—the highest that of 
the London Clay, where the media only has been obsery- 
ed. Mr Mantell mentions a species (not determined) in 
the Chalk of Sussex. M. Deshayes gives us five species 
only, for the two genera Avicula and Meleagrina, four of 
which he cites from the London Clay. Why he should 
not notice the numerous species of Sowerby and Phillips 
I cannot imagine. [am not aware of any species having 
been heretofore observed in our formation. Dr Morton 
mentions his having observed casts in the Green Sand 
of New Jersey. 
FAMILY PECTINIDA. 
GENUS PECTEN. Lamarck. 
P. Deshaysti.* Plate 3. Fig. 66. 
Description. Shell orbicular, rather compressed ; ears 
nearly equal; substance of the shell rather thick ; ribs 
* Named after the distinguished fossil conchologist M. Deshayes. 
