ORISKANY SANDSTONE. 449 



LeptocoBlia flabellites. 



Plate CVI. Fig. 1 a -f; and Plate GUI B. Fig. 1 a -/. 



Jilnfpa Jlahdlilet : Coxrad, Annual Report on the Palaeontology of New- York for 1841, p.55i 

 Lepiocalia propria* : Hall, Regents' Report of 1856, p. 108; Palaeozoic Fossils, 1857, p. 68; 



Shell somewhat semielliptical, varying to suborbicular or transversely 

 oval, generally broader than long. Ventral valve convex, most promi- 

 nent along the middle, declining laterally : beak incurved, with a small 

 round perforation in the extremity, which is completed oil the lower 

 side by the two deltidial pieces ; or, in the absence of these, the fora- 

 men is completed by the umbo of the dorsal valve. Dorsal valve flat : 

 beak straight ; hinge sloping from the beaks at an angle of 110° to 160°, 

 rounded at the extremities. 

 Surface marked by ten to fourteen simple angular plications ; two of 

 which, on the middle of the ventral valve, are a little larger and slight- 

 ly more prominent than the others ; and, between these, there is a third 

 smaller depressed plication, forming an indistinct sinus. On the dorsal 

 valve the two middle plications are a little closer together, and slightly 

 more prominent near the front, than the others; while the depressions 

 separating them from these, each side, are a little wider and deeper 

 than those between the other plications. 



This species presents some varieties of form, apparently dUe to age and other in- 

 fluences; the hinge-line of some individuals being often more extended and more 

 nearly straight. The extension of the beak varies in different individuals, and in 

 those from different localities. The silicified condition of the specimens has obscured 

 the finer surface markings. Many of the specimens appear to retain remains of fine 

 radiating striae; while more distinct concentric lines, and occasional stronger un- 

 dulations of growth, are visible in most of them. 



In specimens from New-York, Maryland and Canada, which I have referred to 

 this species, there are some slight differences which appear to be due to the condition 

 of the sediments in the different localities. 



• I Jiad overlooked the description of Mr. Comsad of A.flabUlitet, as designating this species, at the 

 time I puljllshed the descriptions of new palanozoic fossils; and it is only as these pages are going through 

 the press that my attention has been directed to the subject, leaving no doubt of the identity of the species. 



[ PaljKontolooy III.] 57 



