114 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



valve, and especially in its weaker and fewer (or absent) costae. C. 

 erugatum n. sp. lacks costae, and C. torvum n. sp. has weak costae, but 

 both of these species are larger and have more strongly convex brachial 

 valves than C. evexum, and are proportionately not as wide. C. bow- 

 sheri (Cooper) is similar in outline and in the longitudinal convexity 

 of the brachial valve, but its costae are much stronger on the fold than 

 those of C. evexum, and entirely absent from the flanks. C. evexum 

 attains a larger maximum size. 



Occurrence and abundance. — Chappel Limestone (P. E. Cloud loc. 

 TF-406), 0.55 mile N. 39° W. of High Lonesome Windmill, 8 miles 

 southeast of Brady, Bald Ridge area, McCulloch County, Tex. (50 

 specimens USNM 142150) ; Chappel Limestone (Cloud loc. TF-385), 

 east side of U.S. Highway 87, 6.7 miles south- southeast of Brady, 

 Bald Ridge area, Tex. (2 specimens USNM 142151). 



Age. — Early Mississippian (Kinderhook). 



COLEDIUM EXPLANATUM (McChesney) 



Plate 11, figs. 1-lc ; figures 27, 28 



Rhynchonella explanata McCHESNEY, J. H., 1860 (1859), Desc. new species 



of fossils, p. 50; McCHESNEY, 1865, Plates for new species, pi. 6, fig. 7; 



McCHESNEY, 1868 (1867), Trans. Chicago Acad. Sci., vol. 1, pt 1, p. 30, 



pi. 6, fig. 7. 

 Pugnax explanatus (McChesney) HALL, J. and CLARKE, J. M., 1894, Intro. 



Study of Brach. pt. 2, pi. 44, figs. 14-16; HALL and CLARKE, 1894, Pal. New 



York, vol. 8, pt. 2, pi. 60, figs. 43^5. 

 Camarophoria explanata (McChesney) SCHUCHERT, C, 1897, U.S. Geol. 



Survey Bull. No. 87, p. 162; WELLER, S., 1910, Geol. Soc. America, Bull., 



vol. 21, p. 501, fig. 3; WELLER, S., 1914, 111. Geol. Survey Monogr. 1, p. 173, 



pi. 23, figs. 46-51 ; EASTON, W. H., 1943, Journ. Paleontology, vol. 17, No. 2, 



p. 131. 

 Stenoscisma explanata (McChesney) COOPER, G.A., 1944, Index Foss. No. 



America, p. 315, pi. 120, figs. 41-45. 



Shell about average size for genus, moderately to strongly biconvex ; 

 outline subtrigonal to subpentagonal, small specimens somewhat elon- 

 gate, larger specimens slightly transverse; commissure moderately to 

 strongly uniplicate ; fold high at anterior, also standing fairly promi- 

 nently above flanks, beginning about 5 mm. anterior to brachial beak ; 

 sulcus shallow, broad, beginning about 5 mm. anterior to pedicle beak ; 

 costae strong, rounded to bluntly pointed, beginning about 5 mm. 

 anterior to beaks, numbering two on fold, one in sulcus two to four on 

 each flank ; valves meeting nearly perpendicularly at anterior, without 

 protrusion or trace of stolidium ; growth lines fine, closely spaced ; 

 growth laminae slightly coarser, widely and irregularly spaced. 



Pedicle valve moderately convex transversely, strongly convex 

 longitudinally through sulcus, greatest swelling in umbonal region ; 



