20 Bulletin 5 290 



42 Say 071 Shells, &c. 



markable species ; from which, however, it is sufl&ciently 

 distinct by the much developed form of the lobes. 



In these specimens a considerable portion of the shell 

 remains exhibiting its beautiful iridescent colours. 



Mr. Nuttall gave me the following account of this species. 

 It occurs in the ancient alluvium of the Missouri, or clay 

 formation, reposing adventitiously on the chalk stratum of 

 this region, and imbedded in the indurated shistose beds, 

 amidst other shells, and in the beds which overlie more or 

 less intimately the Xylanthrax or Surturbrand ; they are 

 gradually and regularly acuminated through a length of 

 twelve or eighteen inches, being from three to four inches 

 broad at the base and diminishing to less than half an inch, 

 but a perfect apex or base has not yet been discovered. — 

 They are of frequent occurrence, washed out on the banks 

 of the river, from White river of the Missouri to the Man- 

 dans, but at the same time, locally and not uniformly dis- 

 tributed. 



Genus Ostrea. 



O. convexa, Oval, inequi valve ; inferioj' valve remarkably 

 convex, with a longitudinal indented line on one side, slight- 

 ly auriculated, or rather, angulated each side of the hinge, 

 a longitudinal, tran.sversel}' wrinkled depression, each side 

 before the hinge ; ligament cavity oval, placed beneath the 

 apex ; sitperior valve suborbicular, flat or somewhat con- 

 cave, radicated from the apex to the periphery, annual in- 

 crements strongly marked ; hinge each side before with 

 transverse rugae. 



Length of the convex valve nearly three inches, .breadth 

 two and an half — ^depth about two inches. Cabinet of the 

 Acad. Nat. Sciences. 



A perfect specimen was found by Mr. S. Wetherill near 

 Burlington, N. J. I have since obtained a ferruginated one 

 at Mulliger Hill in the same state. It is remarkable for the 

 great convexity of one of its valves, and by the angles each 

 side of the hinge. — It closely approaches to the genus Gry- 

 phcea ; the lower vah-e is even proportion ably more convex 

 than that of Anomia grypha-a, and is also furnished with the 

 indented line or lateral lobe as in that shell, but the umbo is 

 not prominent, the superior valve is as operculiform as that 



[A. J. S., ist Ser., Vol. II.] 



