134 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



Brachial valve more strongly convex, with greatest convexity about 

 one-third distance anterior from beak ; beak short, with apex hidden 

 by deltidial plates. 



Pedicle valve interior with dental plates meeting to form sessile 

 spondylium in apex of valve, about 1 mm. anterior to apex forming 

 low median septum duplex, elevating spondylium slightly ; median 

 septum extending anteriorly about one-third length of valve, spon- 

 dylium slightly shorter. 



Brachial valve interior with short camarophorium beginning as 

 slight expansion of median septum in apex of valve, height above 

 floor increasing rapidly toward anterior as strongly convex valve and 

 strongly convex camarophorium curve away from one another ; inter- 

 camarophorial plate short, connecting camarophorium to base of hinge 

 plate in apex of valve; hinge plate short, with low cardinal knob at 

 apex, crura extending anteriorly from forward edge of hinge plate, 

 curving with nearly same contour as camarophorium. 



Holotype.—Y.PM. No. 23258, plate 13, fig. lc. 



Comparisons. — Coledium torvum is characterized by its moderate- 

 to-large size for genus, strongly convex brachial valve, and especially 

 by its rather numerous, although weak, costae on the fold and flanks. 

 It differs from smooth C. erugatum n. sp. in possession of costae, and 

 from C. cestriensis (Snider) in its more numerous and weaker costae. 

 It is larger than C. explanatum (McChesney), and also has more and 

 weaker costae and stronger convexity. 



Occurrence and abundance. — Morrow Series at Keough Switch 



Table 29. — Measurements of Coledium torvum from the Morrow Series in 



Oklahoma 



Measurements, in millimeters 



