130 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



549476), and their valves meet at the anterior nearly perpendicularly, 

 rather than nearly in a plane as in the Ontario specimens. The manner 

 of meeting of the valves is more characteristic of a species of Coledium 

 than of a species of Atribonium, to which Fagerstrom's specimens 

 clearly belong. 



Fagerstrom included some of Hall and Clarke's (1894) and Hall's 

 (1894) specimens of C. rhomboidale with his new species Stenoscisma 

 halli Fagerstrom. Direct comparison of the Indiana specimens with 

 Fagerstrom's holotype reveals generic differences. Although the In- 

 diana species is variable, and some specimens have the valves meeting 

 at a larger angle than is typical for Coledium, the Ontario specimen is 

 flattened at the anterior and belongs to the genus Atribonium. Hall and 

 Clarke's species shows the same range of variation as do the National 

 Museum's topotype collection of over 100 specimens. This probably 

 represents a variable population, and in my opinion the species should 

 remain as Hall and Clarke constituted it. 



Occurrence and abundance. — Logansport Limestone, at Pipe Creek 

 Falls, Cass County, Ind. (104 specimens USNM 142468-72); on 

 Pipe Creek, y^ mile northwest of Bunker Hill, Ind. (4 specimens : aff. 

 C. rhomboidale USNM 142473, 74). The Logansport is the "Cor- 

 niferous limestone, Peru, Indiana" of Hall and Clarke (1894) ; the 

 104 specimens are topotypes. 



Age. — Middle Devonian. 



COLEDIUM THERUM (Walcott) 



Plate 16, figs. 1-ld 



Rhynchonella thera WALCOTT, C. D., 1884, U.S. Geol. Survey Monogr. 8, p. 

 223, pi. 7, figs. 6-6c. 



Shell large for genus, moderately to strongly biconvex; outline 

 rounded subtrigonal or subpentagonal to elliptical, greatest width 

 normally slightly anterior to midlength ; commissure uniplicate ; fold 

 moderately high, but not standing prominently above flanks, crest 

 broad, flat ; sulcus shallow, extending anteriorly as tongue into fold ; 

 edges of valves slightly produced in many specimens, forming narrow 

 ridge around anterior margins (probably incipient stolidium) ; costae 

 weak, beginning far forward, about 6-10 mm. anterior to beaks, num- 

 bering two or three on fold, one fewer in sulcus, none to three on each 

 flank, normally much weaker on flanks ; growth lines fine and closely 

 spaced ; growth laminae slightly stronger. 



Pedicle valve moderately strongly convex, greatest swelling ante- 

 rior to beak but just posterior to midlength; beak short, sharp, sub- 

 erect to slightly incurved; beak ridges blunt but distinct in juveniles, 

 rounded and indistinct in large specimens ; delthyrium small, trigonal, 



