BRACHIOPODA—ORTHIDM. 



249 



about two inches, length slightly less. Distinguished from P. 

 nebraskaensis by its less convex pedicle valve, its smaller concentric 

 wrinkles, and especially by having a simple series of small, rather 

 compressed spines without the additional stout and erect series 

 of spines. 



Upper Carbonic of Indiana, Illinois, Iowa and Nebraska. 



Fig. 299. Productus symmetricus. (Ind. Geol. Surv. ) 



ORTHID^E. 



Orthis Dalman. 



Under this name were formerly placed all forms having in general 

 a straight hinge line, cardinal areas well developed in each valve, 

 with usually an open triangular delthyrium in each with deltidium 

 developed only in younger growth stages. Dental lamellae well 

 developed in the pedicle valve and crural plates in the brachial 

 valve. Surface covered with radiating striae or plications. 



This old genus of Orthis has been subdivided into Orthis (re- 

 stricted), Plectorthis, Dinorthis, Hebertella, Orthostrophia, Platystro- 

 phia, Heterorthis, Bilobites, Dahnanella, Rhipidomella, Schizophoria, 

 Ortlwtichia, Enteletes. 



A. Shell surface radially plicate (z. e. , radiating lines coarse) *. 



* Hinge line short (forming about one third the greatest width of shell. Shell 



globular LVII1. Enteletes. 



* Hinge line long I. 



1. Pedicle valve flat or concave. Brachial convex L. Dinorthis. 



1. Pedicle valve convex a. 



a. Brachial valve flat .' XLVIII. Orthis. 



a. Brachial val ve convex l / . 



