Bekde.J Carboniferous Invertebrates. 165 



liquely backward and downward to the middle of the base of 

 each valve : anterior side extremely short, or nearly obsolete, 

 convex, and rounded ; posterior side broader, more compressed 

 or cu lie ate, with its upper edge straight and sloping obliquely 

 backward to the regularly rounded posterior margin ; base 

 broadly and slightly sinuous in the middle, and rounding up- 

 ward at the extremities ; hinge line straight, between one-half 

 and two-thirds as long as the valves, ranging at an angle of 

 about twenty-five degrees with the oblique, longer axis of the 

 shell, so as to meet the sloping upper edge of the posterior 

 margin at a very obtuse but moderately well-defined angle, thus 

 imparting to the somewhat compressed posterior dorsal region 

 a very faintly alate appearance ; beaks extremely oblique, de- 

 pressed nearly to the dorsal margin, very nearly terminal, and 

 scarcely projecting beyond the rounded outline of the anterior 

 extremity. Surface ornamented by about fifteen to twenty ex- 

 ceedingly regular, well-defined, subimbricating, flattened, con- 

 centric ridges or undulations, that gradually become smaller 

 and more closely approximating on the umbones." 



Range and distribution : Upper Coal Measures ; in the oolite 

 at Rosedale and Turner. 



CARDIOMORPHA. 



de Koninck, Anim. Foss. Carb. Belg., p. 101, (1844). 



Cardiomorpha missouriensis. Plate XX, fig. 17. 



Cardiomorpha missourieneis Shumard, Trans. St. L. Acad. Sci., i, p. 



207. (1858); Meek and Worthen, Geol. Surv. 111., v, p. 588, pi. xxvn, f. 8, 



(1873). 

 X ncula merorrrnsis McChesnev, Trans. Chic. Acad. Sci., i, p. 40, pi. n, 



ff. 12a-c, (1868). 

 Nucula cylindrical McChesney, New Pal. Foss., p. 51, (1860). 



Original description : " Shell inequilateral, elliptico-subquad- 

 rate, very thin, length double the height; superior and infe- 

 rior borders subparallel ; cardinal margin long, slightly arcuate, 

 inferior border slightly arched ; anal and buccal margins strongly 

 rounded, the latter being very short ; umbonal region moderately 

 convex in young specimens, and very gibbous in the old, great- 

 est convexity short distance below the beaks ; beaks situated 

 near the anterior margin, rounded, closely incurved and nearly 



