NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA GRANT 1 35 



above Fort Gibson, Okla. (15 specimens), Yale Peabody Museum 

 collection. 



Age. — Early Pennsylvanian (Morrow). 



COLEDIUM UNDULATUM Grant n. sp. 



Plate 14, figs. l-2a ; figure 32 



Shell about average size for genus, strongly biconvex ; outline trans- 

 versely subpentagonal, greatest width posterior to midlength; com- 

 missure uniplicate ; fold high at anterior but not standing prominently 

 above flanks, crest broad and flat ; sulcus broad, shallow, with flattened 

 trough, depressed proportionately to elevation of fold ; costae low, dis- 

 tinct, beginning at beaks or within 5 mm. of beaks, numbering nor- 

 mally three on fold, rarely as many as seven, from three to five on each 

 flank somewhat weaker on flanks; valve edges meeting nearly per- 

 pendicularly, without protruding and without trace of stolidium; 

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

 widely and irregularly spaced. 



Pedicle valve moderately strongly convex, with greatest convexity 

 in umbonal region anterior to beak ; beak short, obtusely pointed, sub- 

 erect to erect ; delthyrium small, trigonal, deltidial plates not observed, 

 probably absent ; pedicle opening through delthyrium, not penetrating 

 apex of valve. 



Brachial valve much more strongly convex, with greatest convexity 

 posterior to midlength, just anterior to beak in umbonal region ; beak 

 curved into pedicle valve. 



Pedicle valve interior with dental plates forming boat-shaped spon- 

 dylium, sessile for fraction of millimeter in apex, from there forward 

 elevated on low median septum duplex, extending anteriorly about 

 one-fourth length of valve. 



Brachial valve interior with camarophorium relatively wide and 

 transversely concave, curving longitudinally toward pedicle valve, 

 trough extending anteriorly about one-third length of valve, somewhat 

 beyond anterior extent of median septum ; hinge plate and crura not 

 observed, due to coarse calcite crystallization of specimens. 



H olotyp e.—USNM 142501, plate 14, fig. 2. 



Growth. — Increase in width and thickness both are accelerated rela- 

 tive to increase in length, with points on both diagrams falling along 

 well defined curved paths (fig. 32). Length and width of median size 

 shells are nearly equal, but larger shells are strongly transverse. Only 

 the largest shells are as thick or thicker than they are long. Projection 

 of the trends toward very small dimensions would continue the even 

 curvature of both curves, with only slight flattening in the length- 

 thickness curve, indicating only minimal allometry in early stages. 



