334 [December, 1843. 



periphery ; margin truncated, direct, tricarinated ; disk and base with sharp 

 prominent transverse sinuous lines. Length, one-third of an inch. 

 Locality, Ibid, (Trenton limestone.) 



Cyrtoceras. 



C. marginalis. Rapidly increasing in size from the apex ; the portion with- 

 out septa straight on the inner margin ; septa closely arranged and slightly sinu- 

 ous ; siphuncle marginal. Length of fragment, four inches; greatest breadth, 

 one and seven-eighths of an inch ; at the smaller end, where it is broken off, 

 half an inch. 



Locality. Ibid, (Trenton limestone.) 



This species does not appear to have been greatly involuted ; about twenty- 

 five septa remain. It is a cast in compact limestone. 



Orthoceras. 



O. annellus. Elongated, tapering, with very prominent, not approximate, 

 acute slightly sinuous transverse ribs, with very fine crowded profoundly wrink- 

 led longitudinal lines; siphuncle submarginal. Length of fragment, one inch 

 and a half ; breadth, half an inch at the larger end ; three-eighths of an inch 

 at the opposite end. 



Locality. Ibid, (Trenton limestone.) 



Inachus. 



I.pervetus. Flattened above and sloping slightly inwards; periphery angu- 

 lated ; from the periphery to the base slightly convex and sloping inwards; base 

 acutely rounded or subangulated. Breadth, one inch and one-third : greatest 

 diamt'er, one-third of an inch. 



Locality. Ibid, (Lead-bearing limestone.) 



TtJRRlTELLA. 



T. . Turritted ; whorls six or seven ; profoundly convex ; rapidly 



increasing in size from the apex. Length, three inches. 



Localities. Mineral Point, Wisconsin, Lewis county, New York. (Trenton 

 limestone.) 



This species occurs in casts, and is the largest shell of a turritted form yet 

 known in the Silurian system of this country. 



CRINOIDEA. 



Pentremites. 



P. truncata. Subovate, or cylindrical ; ambulacra narrow, convex, with dis- 

 tinct numerous rather fine transverse lines; scapula concave, with carinated 

 margins ; base truncated, sides slightly convex, the lower half nearly direct. 

 Length, five-eighths of an inch ; breadth, half an inch nearly. 



Locality. Edwardsville, Madison county, Illinois. 



This species differs from all others that are published in the truncated base, 

 the points of the ambulacrce being on a line with the centre of the pelvis, inde- 

 pendent of the elevation of the alimentary canal. 



