PELECYPODA—PRIONODESMACEA. 



45i 



Avith slightly prominent beaks ; anterior ear minute or wanting. 



Devonic-Cretacic. 



.239. P. hawni Meek and Hayden. (Fig. 595.) 



Carbonic and Permic. 



Posterior ear narrow, obliquely trun- 

 cate. Anterior ear larger. Surface 

 marked with irregular undulating ribs of 

 unequal size and concentric lamellae 

 which at times are very strong over the 

 costae. 



Carbonic: Pennsylvania- Colorado. 

 Permic of Kansas. 



P. kansasensis Beede. (Fig. 



240. 



Fig. 595. 

 awni. (Kan. 



596.) Carbonic and Permic. 



Hinge line nearly straight. Both ears 

 rounded to meet the hinge. Radiating striae wavy. 



Pseudomonotis 

 Pal.," VI/II.) 



Fig. 596. Pseudomonotis kansasensis. (Kan. Pal., VI/II.) 



Coal Measures : Ohio-Colorado and Arizona. Permic of Kansas. 



241. P. equistriata Beede. (Fig. 597.) Carbonic and Permic. 

 Differs from P. hawni in being smaller and shorter, slightly 



more convex, and in having regular striae. 



Pennsylvanic : Kansas, Colorado. Permic : Kansas (Garrison). 



242. P. subcircularis (Gabb). (Fig. 598.) Triassic. 

 Ribs alternating in size. 



