108 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



Table 19. Measurements of Coledium cestriensis from the Pitkin Limestone in 



Oklahoma 



Measurements, in millimeters 



specimens are slightly elongate, and large specimens slightly trans- 

 verse. Projection of the lower ends of both curves toward zero con- 

 tinues the same trends, indicating that proportional growth in early 

 shell stages probably was similar to that in the larger shells available 

 for measurement. 



Comparisons. — Coledium cestriensis is characterized by its large 

 size, two rather weak costae on the fold, and weak or absent lateral 

 costae. It is larger than C. explanatum (McChesney), and has weaker 

 costae on fold and flanks. It is about the same maximum size as C. 

 torvum n. sp., but has weaker and normally fewer costae on the fold 

 and flanks. It also attains about the same maximum size as C. erugatum 

 n. sp., but that species entirely lacks costae. It is smaller, less elongate 

 and more strongly convex than C. therum (Walcott), has fewer costae, 

 and lacks the incipient stolidium that is present sporadically on that 

 species. It differs from C. oh e sum (Clark) from the Mississippian 

 Heath and Brazer Formations (Easton, 1962, p. 42) in its larger size, 

 fewer and weaker costae on fold and flanks, and somewhat narrower, 

 less pronouncedly pentagonal outline. 



This species differs from C. bowsheri (Cooper) from the Magdalena 

 Group of the Sacramento Mountains, N.Mex., in its larger size, pro- 

 portionately narrower outline, much weaker and more variable number 

 of costae that begin farther anterior, and its strong convexity, espe- 

 cially the longitudinal convexity of the brachial valve. 



Occurrence and abundance. — Pitkin Limestone, sec. 35, T-16-N, 

 R-20-E, Muskogee Quadrangle, Okla., Mather's locality 301 (3 speci- 

 mens USNM 92564) ; Fayetteville Shale, on Oklahoma Highway 10, 

 SE.J4 NW.J4 sec. 21, T-15-N, R-20-E, 4 miles southeast of Fort 



