1897.] NEW YORK ACADEMY OF SCIENCES. 267 



differs from S. chesterensis^ as figured b}' Meek and Worthen, * 

 in having the beaks situated nearer the center of the shell and 

 in having the greatest posterior extension of the shell situated 

 more ventrally. 



ScHizoDUS DEPRESSus Worthen. (?) 



PI. XXL, figs. 7-8. 



1884. Schizodus depressus, Worthen^ Bull. No. 2,111. State Mus. 



Nat. Hist., p. 11. 

 1890. Schizodus depressus, Worthen, Geol. Surv. 111., Vol. 8, p. 

 109, PI. 18, figs. 8-8a. 



Shell below medium size, sub-triangular in outline, slightly 

 convex, greatest convexity along the umbonal ridge. Umbonal 

 ridge angular, extending from the beak to the most posterior 

 extension of the shell, sub-parallel with the nearly straight upper 

 portion of the posterior margin of the shell. Beak depressed, 

 obtuse, situated a little anterior to the middle of the shell. 



Hinge-line short. Anterior margin of the shell nearly straight 

 above, sloping venti'ally, regularly rounded below. Ventral 

 margin arcuate. Posterior margin sharpl}- rounded below at 

 the most posterior 'extension of the shell, straight or slightly 

 arcuate above, sloping upward to a point just posterior to the 

 beak. 



The specimens of this species are not well preserved, but as 

 they agree in general form with Schizodus depressus,a.s described 

 and figured by Worthen, they are provisionally referred to this 

 species. They differ from Worthen's figures chiefly in the more 

 obtuse beaks. 



Schizodus? sp. 

 PI. XX., fig. 5. 



Shell below medium size, sub-elliptical in outline, slightly 

 convex in the umbonal region, compressed posteriorly. Beak 

 situated at a little less than one-third the distance from the 

 anterior to the posterior extremit}', incurved and elevated above 

 the hinge-line. Posteriorly from the beak and parallel with the 

 hinge-line is a sharp ridge, the dorsal side of which is a narrow 

 band-like area meeting the hinge-line nearly vertical to the plane 

 of the shell. 



Hinge-line straight, extending from the beak nearly to the 

 posterior extremity. Anterior margin rather sharply but regu- 

 lai'ly rounded ; ventral margin gently arcuate, bending upward 



•Geol. Surv., 111., Vol. 2, p. 301, PI. XXIII., fig. 6. 



