THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY, 



SUPPLEMENT TO VOL. VIII. MARCH 1842. 



LVI. — On a new genus of Fossil Bivalve Shells. By Mr. 



Samuel Stutchbury, F.G.S., A.L.S., &c., Curator of 



the Bristol Institution. 



[With two Plates.] 

 Some years since my attention was called to several species 

 of bivalve shells which were generally placed in the genus 

 Unio ; upon a close examination of many specimens, I was 

 enabled to characterize eight or nine species certainly distinct 

 from any established genus ; also finding that they appeared 

 to be confined to the lias and inferior oolite, which are deter- 

 minate marine beds, I was anxious to remove them from the 

 genus Unio, with which they appeared to have but slight ana- 

 logy- 



With this view I forwarded, in 1837, a paper to the then 

 editor of the c Magazine of Natural History/ which from some 

 cause was not inserted ; but in the meantime the name Pa- 

 chyodon, by which I had designated the new genus, became 

 pretty generally adopted by those who had access to the Mu- 

 seum of the Bristol Institution. I have since been informed 

 that Professor Agassiz has given, or intends to notice the 

 genus under the name of Cardinea: if he has already done so, 

 I shall yield the name Pachyodon, being anxious not to in- 

 crease the already overloaded list of synonyms. 



In the list of genera published in the ' Synopsis of the Bri- 

 tish Museum/ by J. E. Gray, Esq., it is designated by the 

 name of Ginorga, and arranged among the Crassinidte, but no 

 description accompanies the name. 



I have also to observe, that both in the * Mineral Concho- 

 logy ' and in the f Genera of Recent and Fossil Shells/ the 

 Messrs. Sowerby, with their accustomed acumen, had thrown 

 considerable doubt upon the propriety of continuing these 

 several species in the genus Unio. 



PACHYODON. 



Gen. Char. — Shell bivalve, equivalve, inequilateral; hinge con- 

 sisting of a single, oblique, thickened cardinal tooth in the right 

 valve, with a hollow for its reception in the left valve ; anterior la- 

 teral tooth in the right valve obtusely conical ; the posterior lateral 



Ann. §• Mag. N. Hist. Vol. viii. Suppl. 2 I 



