390 Proceedings of the Ohio State Academy of Science. 



PHYLUM MOLLUSCA. 

 CLASS PELECYPODA. 



SCHIZODUS CHE STERENSIS— Meek . nd Worthen. 



1'860. Schisodus Chesterensis. Meek and Worthen, Proc. Acad. Nat. 

 Sci., Phil., p. 457. 

 Upper Chester limestone : Chester, Illinois. 

 1866. Schisodus chesterensis. Meek and Worthen, Geol. Surv. Ill, VoL 

 II, p. 301, pi. 23, figs. 6a, b. 

 Chester group: Chester, Illinois. 

 1891. Schisodus Chesterensis. Whitfield, Ann. N. Y. Acad. Sci., VoL 

 V, p. 587, pi. 14, fig. 4. 

 Maxville limestone : Maxville, Ohio. 

 1895. Schisodus Chesterensis. Whitfield, Geol. Surv. Ohio, Vol. VII, 

 p. 474, pi. 10, fig. 4. 

 Maxville limestone : Maxville, Ohio. 



Description. — "Shell of medium size, transversely sub- 

 ovate, with moderately convex valves and large, strong, in- 

 curved, and projecting beaks. Anterior end forming one-third 

 the length of the shell, inflated, and rapidly sloping from the 

 beaks to the longest point, which is near the middle of the 

 height, and rounding backward below ; posterior end elongated 



Fig. 16. — Schisodus chesterensis. A view of the left valve. (After 

 Whitfield.) 



and narrowed, obtusely pointed at the extremity; basal margin 

 irregularly convex, most strongly arcuate opposite the beaks ; 

 posterio-cardinal margin sloping somewhat rapidly from the 

 beaks backward, and the cardinal slope rather abrupt. Surface 

 of the shell smooth, except for the fine lines of growth [Whit- 

 field, 1895]." 



