INVERTEBRATES. 155 



Genus SPIRIFER, Sowerby, 1815. 



(Mineral Coch., ii, p. 42.) 

 Subgenus MARTINIA, McCoy. 



Martinia, McCoy, 1844. Carb. Foss. Ireland, p. 139. 



Ambocmlia, Hall, 1860. Thirteenth Ann. Report Regents Univ., N. Y., p. 71. 



Spirifer cooperensis, Swallow. 



PI. 14, Fig. 5 a, 5 6. 



Spirifer Cooperensis, Swallow, 1860. Trans. St. Louis Acad. Sci., Vol. 1, p. 643. 

 Spirifer semiplicata, Hall? Dec, 1860. Thirteenth Ann. Report of the Regents Univ. 

 N. Y., p. 111. 



Shell small, transversely subelliptical, gibbous, greatest 

 breadth generally a little above the middle; lateral margins 

 rounded, converging somewhat towards the front, which is sub- 

 truncate or slightly sinuous in the middle ; hinge considerably 

 shorter than the breadth of the shell, rounded at the extremi- 

 ties. Dorsal valve depressed-convex, provided with a low, 

 scarcely defined mesial elevation, on each side of which are 

 two or three depressed, rounded, obscure plications, rarely 

 traceable to the umbo; beak nearly obsolete, or very small, 

 and scarcely distinct .from the cardinal margin; area small, not 

 incurved. Ventral valve considerably more gibbous than the 

 other, provided with a moderately distinct shallow mesial sinus, 

 which commences very narrow near the beak, and widens 

 rather rapidly to the front, its deepest part being along the 

 middle; lateral slopes on each side of the sinus, having three 

 or four very obscure, depressed plications, similar to those on 

 the other valve ; beak prominent, distinctly incurved beyond 

 the hinge line ; area small, triangular, arching back over the 

 hinge, moderately well defined; foramen triangular, nearly as 

 wide at the hinge line as on each side, apparently always open. 

 Surface having a few subimbricating concentric marks of 



