148 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



Subfamily BILLINGSELLIN.^ Schuchert, 1893 



Primitive Orthacea very much like Nisusiiiiae but without true 

 spond34ia and cruraha. There is a more or less well-developed car- 

 dinal process except in Lower Cambrian forms. 



Wijiianclla 



Billingsella 



Orusia 



Otusia 



Wynnia 



Subfamily EOORTHIN^ Walcott, new 



Derived Orthacea nearly always wath large open delthyria; del- 

 tidia and chilidia occasionally retained throughout life, but more 

 often only in the younger growth stages. Cardinal process well de- 

 veloped. Shell structure dense, granular, and with punctate lamellae. 

 Boorthis 

 Finkelnhnrgia 



Superfamily STROPHOMENACEA Schuchert, 1896 



Derived, progressive, terminal Protremata, out of Orthacea (Bil- 

 lingsellidse). Deltidia and chilidia nearly always well developed. 

 Cardinal process always well developed. 



Family STROPHOMENIDiE King, 1846 



Subfamily RAFINESQUIN^ Schuchert, 1893 



Strophomenoids having generally a convex ventral and a concave 

 or nearly flat dorsal valve. 

 Bostrophomena 



Superfamily PENTAMERACEA Schuchert, 1896 (emend) 



Specialized Protremata with well-developed free or supported 

 spondylia and cruralia. Deltidia and chilidia usually absent. 



Family SYNTROPHIID^ Schuchert, 1896 



Primitive Pentameracea with long, straight cardinal areas. 

 (?) Szvantonia 

 Syntrophia 

 H II en ell a 

 Clarkella 



