PELECYPODA—TELEODESMA CEA . 533 



Distinguished from C. vejitricosa by its regular, concentric ribs, 

 instead of mere striae. 



Montanan : South Dakota, Montana, Assiniboia. 



Order 3. TELEODESMACEA. 



CXXXI. Pleurophorus King. 



Inequilateral, elongated, rectangular, with beaks nearly terminal. 



Two cardinal and one posterior lateral tooth present in each valve. 



Anterior muscle scar deep, bounded posteriorly by a ridge. Pallial 



line simple. Devonic-Triassic. 



474. P. tropidophorus Meek. (Fig. 724.) Carbonic. 

 Posterior slope doubly angular with two ridges that pass ob- 

 liquely backward from the beaks. Surface marked with strong 

 concentric growth lines. 



Coal Measures of Ohio, Missouri. 



475. P. oblongus Meek. Carbonic. 

 Somewhat similar to P. tropidophorus but differs in the small 



size, with length never exceeding .5 inch, in the wider posterior 



Fig. 724. Pleurophorus tropidophorus, right valve. (Kan. Pal., VI/ II.) 

 Fig. 725. Pleurophorus subcostatus, left internal mold. (Kans. Pal., VI.) 

 Fig. 726. Pleurophorus albequus, right valve. (After Beede.) 



end, producing a slight divergence of the basal and cardinal mar- 

 gins, in lacking the doubly angular slope and in the finer concen- 

 tric striae. 



Illinois, Missouri, Arkansas, Nebraska. 



476. P. subcostatus Meek and Worthen. (Fig. 725.) 



Carbonic. 

 Surface covered with fine growth lines and with three or four 

 radii extending from the beak to the posterior margin. 

 Ohio-Colorado. 



477. P. occidentalis Meek and Hayden. Carbonic and Permic. 

 Much like P. oblongus in size but with narrowing posterior end 



instead of the vertically truncate end of P. oblongus and with radi- 

 ating ridges extending from the beak to the posterior margin. 



Carbonic : Nebraska, Colorado. Permic : Kansas, Nebraska, 

 Texas, New Mexico. 



