TO GEOLOGY. 87 



having a smaller hinge. One of trie 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 observ 

 ed. Mr Mantell mentions a species (not determined) in 

 the Chalk of Sussex. M. Deshayes gives us five species 

 only, for the two genera Jlvicula and tMeleagrina, four of 

 which he cites from the London Clay. Why he should 

 not notice the numerous species of Sowerby and Phillips 

 I cannot imagine. I 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. Deshaysii* 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, 



