COAL-MEASURE SPECIES. 337 



This fine species agrees in size and form, perhaps, more nearly with 

 the well known European Permian species, S. obscurus, Sowerby, than 

 with any other described species, though in some respects it is, perhaps, 

 more nearly related to S. truncatus. It attains a considerably larger size, 

 however, than even S. obscurus, from which it dififers in having its beaks 

 more elevated, and without any backward inclination. Its valves are 

 also proportionally less convex, and have the anterior margin less prom- 

 inently rounded in outline, while its posterior ventral margin shows not 

 a trace of the sinuosity said to become more conspicuous in that species 

 in large, mature specimens. In the latter character it differs still more 

 decidedly from S. Schotheimi, of Geinitz, as well as in its less elongated, 

 more inequilateral form, and higher beaks. Its much larger size, more 

 compressed form, more elevated beaks, and shorter anterior side, distin- 

 guish it from S. truncatus, King. 



I know of but two other American species that attain so large a size 

 as this. These are S. amplus, M. and W., and S. occidentalis (=Cypricardia 

 occidentalis, Swallow), both of which are from the Coal Measures. 'Com- 

 pared with the former, it is at once distinguished by its much more 

 elevated beaks, decidedly narrower and truncated posterior side, and sub- 

 angular posterior umbonal slopes. In some of these characters it agrees 

 more nearly with Prof. Swallow's species, while in other respects it dif- 

 fers far more widely, that shell being very much more ventricose, with 

 a greatly more sloping posterior dorsal outline, less truncated posterior 

 margin, and distinctly sinuous posterior basal margin, more angular pos- 

 terior basal extremity, and more prominentjy rounded anterior basal 

 outline. 



I have before me, from the Upper Coal Measures at Nebraska City, 

 Nebraska, a very similar form, differing only in its smaller size, more 

 nearly central beaks, and much more prominent ventral and anterior 

 margins. It is, however, probably a distinct species. 



Locality and position : Putnam Hill and Flint Ridge, Ohio. Lower Coal Measures. 

 Prof. Andrews's collection. 



AvicuLOPiNNA Americana, Meek. 



Plate 20, fig. 2. 



Avicula pinnseformis, Geinitz (1866) ; Carbonif. und Dyas in Nebraska, 31, tab. II., fig. 



13 (not Avicula pinnieformis, Geinitz, 1857). 

 Aviculopinna Americana, Meek (1867) ; Am. Jour. Sci, and Arts, XLIV., 282, and (1872) 



Pal^eont. Eastern Nebraska, in Hayden's Report of Geol. Survey of Nebraska, 197. 



Shell small, compressed, with the general form of a narrow Pinna; 

 ventral margin ascending very gradually forward, and nearly or quite 



22 



