126 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



Discussion. — This species is represented in the U.S. National Mu- 

 seum collections by only a dozen specimens, about one-third of them 

 well-preserved. It is described despite the small collection because all 

 of the important features are shown, the species is distinctive, and it 

 is one of the few stenoscismatids known from the Pennsylvanian. 



Occurrence and abundance. — "Upper Carboniferous," Chariton 

 County, Mo. (12 specimens USNM 24405). 



Age. — Pennsylvanian. 



COLEDIUM RHOMBOIDALE (Hall and Clarke) 



Plate 10, figs. 1-la; plate 11, figs. 2-7; figure 30 



Camarophoria rhomboidalis HALL, J., & CLARKE, J. M., 1894, Pal. New York, 

 vol. 8, pt. 2, p. 366, pi. 62, fig. 25-29; HALL, J., 1895, 14th Ann. Rept. State 

 Geologist, New York, p. 363, pi. 9, fig. 37-40. 



NOT Stenoscisma rhomboidalis (Hall and Clarke) FAGERSTROM, J. A., 

 1961, Journ. Paleontology, vol. 35, No. 1, p. 29, pi. 9, fig. 45-47. 



Shell somewhat small for genus, moderately to strongly biconvex; 

 outline subtrigonal, normally slightly elongate, less commonly equi- 

 dimensional, rarely transverse, normally widest anterior to midlength ; 

 commissure uniplicate ; fold moderately high, projecting above flanks 

 only near anterior, not prominently, beginning about 5 mm. anterior 

 to brachial beak; sulcus shallow except at anterior, there depressed 

 below flanks, projecting as broad tongue into fold; beginning about 

 6 mm. anterior to pedicle beak; costae moderately strong, crests 

 rounded, beginning about 4 mm. anterior to beaks, numbering two or 

 three on fold, one fewer in sulcus, from one to three on each flank; 

 valves meeting nearly perpendicularly at anterior, some specimens with 

 slightly larger angle, but not enough to produce flattened anterior; 

 growth lines fine, closely spaced ; growth laminae slightly stronger, 

 irregularly spaced. 



Pedicle valve moderately convex, greatest swelling anterior to beak 

 in posterior part of valve ; beak short, sharp, somewhat attenuate, sub- 

 erect to slightly incurved ; beak ridges rounded, distinct on some speci- 

 mens, obscure on others; delthyrium triangular, nearly filled by bra- 

 chial beak ; deltidial plates not observed, very small if present ; foramen 

 small, not penetrating apex of beak. 



Brachial valve much more strongly convex transversely, moderately 

 convex longitudinally along fold, greatest convexity posterior to mid- 

 length, anterior to beak ; apex of beak within pedicle valve. 



Pedicle valve interior with dental plates forming boat-shaped 

 spondylium, sessile on floor of valve for at least 1 mm. in apex, as 

 much as 2.5 mm. in some specimens, then elevated on low median 



Fig. 30. — Scatter diagrams of dimensions of Coledium rhomboidale (Hall and 

 Clarke) from Pipe Creek Falls, Ind. 



