CLASSIFICATION. 325 



Superiamily DISCINACEA Waagen [1885]. 

 (Emended Schuchert [1897, p. 130] and Walcott [1908e, p. 146].) 



Derived Neotremata with phosphatic shells, a listrium modifying the pedicle slit, and 

 without pseudodeltidia and false cardinal areas. Dorsal protegulum usually subcentral. 



Family DISCINID.ffi Gray [1840]. 

 (Emended Schuchert [1897, p. 130] and Walcott [1908e, p. 146].) 



Discinacea with an open pedicle notch in early life in the posterior margin of the ventral 

 valve, which is closed posteriorly during neanic growth, leaving a more or less long, narrow 

 slit partly closed by the listrium. 



Orbiculoidea d'Orbigny [1847]. 



Superfamily CRANIACEA Waagen [1885]. 



Cemented calcareous specialized Neotremata without pedicle or anal openings at maturity. 



FamUy CE,AimD.ffi King [1846J. 



Craniacea with the pedicle functional probably onlj^ during nepionic growth. 

 PMRedra Koken [1889, pp. 465, 467]. 



Order PK.OTK.EMATA Beecher [1891, p. 355]. 

 (Emended Schuchert [1897, p. 131] and Walcott [1908e, p. 147].) 



Progressive (though atrematous Kutorginacea), articulate calcareous Bracliiopoda with 

 well-developed cardinal areas. The pedicle opening is restricted to the ventral valve through- 

 out life or during early growth, and is often modified and more or less closed by a deltidium. 

 Often there is a cliilidium. Bracliia unsupported by a calcareous skeleton other than crura. 



Superfamily ORTHACEA Walcott and Scliuchert [Walcott, 1908e, p. 147]. 



Derived, progressive Protremata. Cruralia and rudimentary spondylia (pseudospon- 

 dylia) free or cemented (through sessility) directly to the valves. Sometimes without deltidia 

 and chilidia. Cardinal process more or less well developed except in the most primitive genera. 



FamUy BILLIITGSELLID.ffi Schuchert [1893, p. 152]. 

 (Emended Schuchert [1897, p. 132] and Walcott [1908e, p. 147].) 



Primitive Orthacea with an open or more or less closed delthyrium. Cardinal process well 

 developed, rudimentary, or absent. Usually with a clearly defined pseudospondylium, to which 

 the muscles of the ventral valve were attached. Shell structure dense, granular, lamellar, 

 nonfibrous. 



Subfamily NISTTSIIN.ffi Walcott and Schuchert [Walcott, 1908e, p. 147 



Primitive Orthacea with more or less well-developed deltidia and with or without rudi- 

 mentary cliilidia. Spondylia and cruralia rudimentary or small and not supported by septa. 

 Cardinal process rudimentaiy or absent. 

 Nisusia Walcott [1905a, p. 247]. 



(JameseUa) Walcott [1905a, p. 252]. 

 Protorthis Hall and Clarke [1892c, p. 273]. 

 (Loperia) Walcott [1905a, p. 287]. 



SubfamUy BILLINGSELLItf.ffi Walcott [1908e, p. 148].<i 



Primitive Orthacea very much like Nisusiinaj, but without true spondylia and cruralia. 

 There is a more or less well-developed cardinal process except in Lower Cambrian forms. 

 Wimanella Walcott [1908d, p. 98]. 

 Billingsella Hall and Clarke [1892b, p. 230]. 

 Orusia Walcott [1905a, p. 27.3].. 

 Otusia Walcott [1905a, p. 246]. 

 Wynnia Walcott [1908e, pp. 142 and 148]. 



o This subfamily is wrongly referred to Schuchert, 1893, by Walcott [IQOSe, p. 148). 



