454 Trans. Acad. Set. of St. Louis. 



the margin of the shell and which usually become stronger 

 and more or less irregular above the shallow byssal sinus. 

 Hinge arcuate with a blunt, tooth-like callosity beneath the 

 beake in the right valve. 



The dimensions of a large right valve are: length 22 mm., 

 width 15.5 mm., convexity 7 mm.; those of a smaller left 

 valve are: length 17 mm., width 11.5 mm., convexity 5 mm. 



Bemarks. This species has its nearest relative in the little 

 shell described as Modiomorplia northvievjensis Weller, from 

 the Northview sandstone of southwestern Missouri.* The 

 two shells are certainly cogeneric, and it is possible that if 

 more perfect material from the Northview sandstone could be 

 had, they would prove to be the same species. The North- 

 view species, of which a single specimen has been observed, is 

 less strongly convex and is proportionally somewhat wider 

 posteriorly than the shells from Glen Park, and for the pres- 

 ent the two species will be considered as distinct. The refer- 

 ence of the species to the genus Modiola must be considered 

 as tentative; it agrees more closely with this genus than with 

 any other, but should possibly be considered as distinct on 

 account of its hinge structure. 



CyPRICARDINIA 8UBCUNEATA n. Sp. 

 PlaU 2, figs. 18-19, 



Description. Shell small, subovate to subelliptical in out- 

 line, length about twice the width, beaks nearly terminal. 

 Dorsal margin nearly straight or slightly arcurate from oppo- 

 site the beak to the posterior extremity of the hinge-line, 

 posterior margin meeting the dorsal margin in an obtusely 

 rounded angle, sloping obliquely backward and downward 

 with a slightly convex curve to the sharply rounded, subcu- 

 neate postero-ventral margin, ventral margin subparallel with 

 the dorsal, slightly sinuate near the middle and curving rather 

 abruptly upward in front into the short, sharply rounded an- 

 terior margin. Valves strongly convex, umbonai ridge 

 arcuate, well defined, extending from the beak to the postero- 

 ventral margin ; the surface sloping abruptly from the um- 



• Trans. Acad. Sci. St. Louis, vol. 9, p. 28, pi. 4, fig. 19. 



