BEEDE: UPPER PERMIAN RED BEDS. 157 



raentary for specific determination. Length of specimen 

 from point of broken beak, 17 mm. 



Whitehorse spring, Oklahoma; very rare. 



This shell seems to be closely related to M. permiana and 

 M. cuneiformis Girty, so far as general form goes. It may be 

 identical with the latter, but I think it is not. 



SCHIZODUS OVATUS Meek?. 



Plate VII, figures 7, 76. 



Shell of moderate size ; not very convex ; hinge rather 

 short; beaks prominent; umbonal ridge well defined, sub- 

 angular ; relation of height to length in perfect specimens 

 probably a little less than three to five. Anterior outline 

 from beak downward ovate ; ventral border elliptical ; pos- 

 tero-ventral border semitruncate, posterior nearly straight. 

 The beaks are incurved. Some of these specimens show 

 traces of concentric undulations. Three specimens. Height, 

 18, 14, 18 mm. ; length, 26, 19, 23.5 mm., respectively. 



Whitehorse spring, Oklahoma; common. Dozier, Tex.; 

 rare. 



The Schizodus material in these collections is unsatisfaqtory. 

 In the previous paper there were two species represented. 

 However, they were destroyed in the fire at University of 

 Oklahoma, and good material is wanted in our collections, 

 except for immature specimens, which are not satisfactory in 

 critical work. 



SCHIZODUS? OKLAHOMAENSIS, n. sp. 



Plate VII, figure 6. 



Shell rather small and schizodiform. Beak very promi- 

 nent, highly elevated, rather sharp, nearly vertical, almost 

 centrally located, and curving inward. The hinge is com- 

 paratively short, so far as shown in the specimen. Posterior 

 umbonal ridge very prominent. The anterior margin slopes 

 obliquely downward from the beak, and rounding sharply 

 into the elliptically curved ventral margin. Postero-ventrally 

 the margin curves abruptly upward at the foot of the umbonal 

 ridge, making the lower posterior border truncate, the upper 

 portion bending to the hinge at an obtuse angle. The con- 

 vex portion of the shell is marked with heavy undulations, 



