416 PALEONTOLOGY OF NEW YORK. 



forms are usually longer than wide, the Western ones are as long as wide, and 

 sometimes wider, and the cardinal extremities are usually extended and frequently 

 mucronate. They are likewise less ventricose, the space between the valves being 

 less, and the muscular impressions not so strongly marked. In these respects, 

 however, the New York specimens of the Chemung group more nearly resemble 

 the Western ones. 



Geological formaiion and locality. In rocks of the age of the Hamilton group, 

 at Eock Island, 111., and at Independence and New BuflUlo, Iowa. 



Spirifcra iiiaia. 



PLATE LXIII, FIGS. 6-13. 

 jithyrit maia : Bilunqs. Canadian Jour. Ind. Sci. and Arts, May, 1860, p. 276. 



Shell below the medium generic size, ventricose, wit^ rounded cardinal 



angles, giving a longitudinally ovate outline, with a depressed subglobose 



form ; hinge line very short ; cardinal area narrow and sometimes hidden 



by the beak. 



Dorsal valve suborbicular, moderately ventricose, with a distinctly elevated 



rounded mesial fold. 

 Vkntrax valve more ventricose than the opposite, with a large, tumid 



incuired beak, and a moderate, subangular mesial sinus. 

 Surface destitute of plications, but marked by more or less distinct concen- 

 tric striae of growth. 



This species is of the type of, and in some conditions greatly resembles, S. lineata, 

 of the Coal measures, but differs in the projecting beak and more ventricose dorsal 

 valve, as also in the surface markings. It is also very similar to S. suhumbona, 

 of the Marcellus shale, but is a larger form, and differs in the shorter hinge line, 

 larger beak and more ventricose dorsal valve, and in the surface markings. 



Geological formation and locality. In the Corniferous limestone of Ohio and 

 Canada West. The specimens figured are from Rev. H. Herzer, of Columbus, Ohio. 



