292 PALAEONTOLOGY OF OHIO. 



the name S. biplicatus, the identification has not been made from direct 

 comparison with authentic specimens of that shell. I also think it very 

 jjossible that S. Osagensis, Swallow, is only a more gibbous form of this 

 shell, with less extended lateral angles. At any rate, there are speci- 

 mens among the Ohio collections agreeing pretty nearly with the descrip- 

 tion of S. Osagensis, that seem to be connected with the form figured on 

 our plate by intermediate varieties. I much regret that the circum- 

 stances elsewhere explained prevented me from giving full illustrations 

 of both valves, as well as of the different varieties of this shell. 



Locality and position : Upper members of the Waverly group, at Richfield, Ohio. 

 rs at the same horizon in Iowa, and probably in Missouri and Illinois. 



LAMELLIBRANCHIATA. 



Genus ENTOLIUM, Meek. 

 (Cal. Geol. Kept., II., 479.) 



Entolium Shumardianum, Wincliell? (sp.) 



Plate 15, figs. 4a, b. 



Pernopecten Shumardianus, Winchell (1865); Proceed. Acad. Nat. Sci., Philad.,XVII., 



126. 

 Compare P. Umatus, Winchell (1865), lb., and Avlcula Cooperensis, Shumard (1855), 



Missouri Geol. Report. 



Shell compressed-lenticular, thin, nearly equivalve, suborbicular ex- 

 clusive of the ears; basal margin rounded; lateral margins rounded or 

 with the posterior one sometimes slightly truncated or straightened on 

 the upper slope, both apparently a little gaping above the middle ; um- 

 bonal slopes straight and converging to the beaks at an angle of about 

 115°; hinge margin very short, or scarcely equaling two- fifths of the 

 greatest breadth of the valves below, in the left valve sloping very 

 slightly inward from the extremities of the ears to the beak at the mid- 

 dle, but in the right valve straight; ears small, flat, triangular, equal, or 

 very nearly so, and obtusely angular at the extremities, without any 

 traces of a byssal sinus under them on either side ;* beaks small, equal, 



■'••The ears are not represented quite obtuse enough in our figure 4a. If their lat- 

 eral margins were continued up from below straight (but obliquely), so as to intersect 

 the hinge margin above at an angle of about 100°, instead of being a little sinuous, 

 they would be correct. The same objection also applies, though in a less marked de- 

 gree, to figure 46. 



