178 MISSISSIPPIAN BRACHIOPODA 



Pedicle valve convex in the umbonal region, the surface curving ab- 

 ruptly to the postero-lateral margins and sloping with a gently convex 

 curvature to the antero-lateral margins or, sometimes becoming a little 

 concave as it approaches the margin, from beak to front along the median 

 line the curvature of the surface is nearly a semicircle ; mesial sinus orig- 

 inating near the middle of the valve, of only moderate depth, nearly flat, 

 or sometimes gently convex across the bottom transversely, produced an- 

 teriorly in a rather broadly rounded or truncate lingual extension, the 

 beak sharply pointed and incurved, obscuring the delthryium. Surface 

 marked by sharply angular, simple plications which originate at the beak, 

 there being from four to six on the bottom of the sinus and about five on 

 each lateral slope of the valve, the largest plications of the valve are those 

 bounding the sinus, those of the lateral slopes growing rapidly smaller, 

 the last one towards the cardinal extremities being very faint or almost 

 obsolete. Internally the dental lamella? are of moderate length and but 

 slightly diverging anterior. 



Brachial valve more convex than the pedicle, the greatest depth near 

 the anterior margin, posteriorly from the point of greatest convexity the 

 surface slopes with a very gently convex curvature which becomes 

 rapidly more convex in the posterior half of the distance, anteriorly from 

 the same point the curvature is short, and abrupt, laterally the surface 

 curves rather abruptly to the margins .from the median portion of the 

 valve which is gently convex transversely; mesial fold originating near 

 the middle of the valve, not conspicuously differentiated from the gen- 

 eral convexity except towards the anterior margin; beak pointed and 

 strongly incurved beneath that of the opposite valve. Surface marked 

 by simple plications similar to those of the opposite valve but a little less 

 angular. Internally a median septum reaches anteriorly from the beak 

 for about one-third the length of the valve, this septum divides internally 

 in the manner characteristic of the genus, forming a crural cavity between 

 the margins of the divided hinge-plate. 



Minute surface markings obscure upon the specimen studied. 



Remarks. The above description of this species has been prepared from 

 specimens collected by Professor Rowley from the original locality and 

 identified by him as being members of his species, specimens which are, 

 therefore, metatypes. The species is characterized by a width greater 

 than its length, its angular plications, and the variable number of plica- 

 tions in the sinus. It differs from C. tuta, which is associated with it at the 

 type locality, in its greater proportional width, its more angular plications, 

 and the greater depth of the sinus in front. 



Horizon. Lower Burlington limestone (white chert.) 



