SPIRIFER 307 



species may be differentiated. In none of the casts of this species which 

 have been examined, has any punctate structure of the shell been ob- 

 served, but this shell structure is almost without exception well shown 

 upon the casts of C. neogenes by the fine papillae which are the casts of the 

 original perforations of the shell. The fine surface markings have not 

 been observed in this species because of the lack of proper external im- 

 pressions of the shell, such as have been seen of C. neogenes. The species 

 was clearly well marked by concentric growth lines, but it is not known 

 that they were such strongly lamellose and regular markings as are 

 characteristic of many species of Delthyris. It is believed that this was 

 their character, a character which, in the absence of a punctate shell 

 structure, would throw the species into the genus Delthyris rather than 

 Spiriferina. 



Horizon. Residual chert, probably of Keokuk age. 



Genus SPIRIFER Sowerby 



Description. Shells varying in size from small to very large, usually 

 wider than long, rarely longer than wide, the hinge-line straight, 

 shorter than the greatest width of the shell and the cardinal extremities 

 rounded; or more frequently the greatest width of the shell along the 

 hinge-line and the cardinal extremities angular and more or less extended, 

 sometimes conspicuously acuminate. Mesial sinus in the pedicle valve 

 and fold in the brachial valve usually well developed, more rarely with- 

 out fold or sinus. Surface of both valves marked by radiating plications 

 which may be simple without division from the point of origin at 

 the cardinal margin to the anterior margin, or may divide in various 

 manners; the plications may be present upon the lateral slopes only or 

 upon both the lateral slopes and the fold and sinus. Besides the plica- 

 tions the surface may also be marked by fine, radiating striae or by fine 

 or coarse concentric growth lines, or by both radiating and concentric 

 markings. The pedicle valve with the beak variously elevated above 

 the hinge-line and variously incurved, the cardinal area varying from 

 very narrow to high, usually arched but sometimes nearly or quite flat, 

 the delthyrium rather broadly triangular and open; the surface of the 

 cardinal area is transversely striate and the inner shell layers bear a 

 series of vertical canals at whose extremities along the hinge-line the 

 shell tissue is sometimes produced in a row of denticles which articulate 

 with a row of pits in the opposite valve. Internally the hinge-teeth are 

 strong and are supported . by short dental lamella? ; the muscular area 

 is of moderate size and is often deeply impressed, ovate or obcordate in 

 outline, occupied in large part by the diductor scars which are usually 

 marked by radiating or branching furrows. The brachial valve with a 

 very narrow cardinal area divided by a broadly triangular delthyrium; 

 the cardinal process is a low, transverse, sessile apophysis with its surface 



