86 CONTRIBUTIONS 



exists in Derbyshire in the first mentioned formation, and 

 twenty-seven others in the superior beds of England. Five 

 of these are from the London Clay. M. Deshayes gives 

 us twenty-three from the Tertiary of Europe. Six of these 

 are from the Paris basin. Mr Say describes two species, 

 the Icevis and concentrica from the Tertiary of Maryland, 

 and Mr Conrad two from the Tertiary of Claiborne. 



ORDER CONCHIFERA UNIMUSCU- 

 LOSA. 



FAMILY MALLACEA. 



GENUS AVICULA. Lamarck. 



Jl. Claibornensis. Plate 3. Fig. 65. 



Description. Shell thin, thickened along the dorsal 

 margin, acutely angular before ; beaks small, pointed ; 

 teeth small and placed near the anterior margin ; wings 

 very oblique ; nacre very pearly. 



Diam Length .... Breadth . . . : k 



Observations. Several fragments and one nearly com- 

 plete valve only were received by me. From these, I am 

 unable to identify it with any other species. It differs 

 from the A. media (Sowerby), in being more oblique and 



