GENERA OF THE SUBORDER ORTHOIDEA 



Subfamfly TAFFIIN^ Schuchert and Cooper 1931 



Aberrant Orthidx having a sub-rafinesquinoid habit, 

 with an orthoid interior. Has the following genera: 

 Tafia Ulrich and Eostrophonwna VValcott. 



Genus TAFFIA Ulrich 1926 

 PI. 16, fig. 11 



Ulrich in Butts, Gcol. Surv. Alab.ima, Special Rept. 14, 

 1926, p. 99, pi. 18, figs. 13-17 (figs. only). 



Genoholotype. — T. flanoconvexa Butts 1926. 



Description. Exterior. — Rafinesquinoid in out- 

 line ; lateral profile plano-convex to slightly concavo- 

 convex. Ventral interarea long, slightly apsacline or 

 orthocline ; delthyrium closed by a non-perforate del- 

 tidium; dorsal interarea anacline; notothyrium closed 

 by a complete chilidium. Surface multicostellate. Shell 

 substance fibrous, impunctate. 



Ventral interior. — Delthyrial cavity deep; teeth 

 large; dental plates short, obsolete in old shells. Mus- 

 cle marks confined to the delthyrial cavity. Pallial 

 trunks divergent, not unlike those of BilLingsella. 



Dorsal interior. — Notothyrial cavity shallow ; noto- 

 thyrial platform thick, with or without a simple orthoid 

 cardinal process. Brachiophores as in Orthis s. s., 

 short, and supported by the addition of callus spread- 

 ing from the notothyrial platform. 



Geologic range. — Lower Ordovician or Cana- 

 dian (Odenville) of Alabama, and British Columbia. 



Species 



Tafia flanoconvexa Butts 1926 

 Protorthis tones Walcott 1924 

 P. forcias Walcott 1 924 



Distinguishing characters. — Tafia may be 

 recognized by its rafinesquinoid outline and profile, 

 the prominent imperforate deltidium and complete chil- 

 idium, and, inside the dorsal valve, by its similarity to 

 Orthis s. s. 



Discussion. — Externally and internally Tafia ap- 

 pears to be most closely related to Eostrophomena of 

 the Lower Ordovician of Europe. The European 

 genus is not well known, but a study of the genotypes 

 does not reveal the presence of a cardinal process. 

 Among the early brachiopods, however, the presence 

 or absence of a simple ridgelike cardinal process seems 

 to be of little taxonomic significance. 



Genus EOSTROPHOMENA Walcott 1905 



Walcott, Proc. U. S. Nat. Mus., vol. 28, 1905, p. 256; 

 Camb. Brach., 1912, p. 795, pi. 95, figs. 6-6b. 



Genoholotype. — E. elegantula (VValcott) 1905. 



Discussion. — VValcott applied this name to small 

 shells with a rafinesquinoid outline and profile. The 

 ventral valve is moderately convex and the dorsal is 

 gently concave. The ventral valve has a low fold 



and the dorsal is provided with a low sulcus. The 

 valves are unequally multicostellate, fine costella; being 

 numerous and concentrated between more elevated, 

 distant coarse ones. A dorsal interior figured by Wal- 

 cott shows a rather strong median elevation separating 

 a quadripartite adductor field. The divergent ends of 

 the brachiophores are barely visible and evidently they 

 enclosed a fairly elevated notothyrial platform. He 

 describes the cardinal process as "more like that of 

 Orthothetcs than that of Strophomena ; it differs from 

 both in being more simple in its construction." 



The junior author examined the types of E. ele- 

 gantula in the U. S. National Museum and does not 

 concur with Walcott's conclusion in regard to the 

 cardinal process. His figure (1912, pi. 95, fig. 6b) 

 does not show a cardinal process at all, and the speci- 

 men does not show an interarea. The notothyrium is 

 covered by matrix so as to conceal the cardinal process 

 if any be present. 



Walcott suggests Strophomena aurora Billings as 

 congeneric with Eostrophomena, and in this the writers 

 agree. According to Billings, however, this species has 

 a simple orthoid cardinal process, and its only stro- 

 phomenoid feature is a sparsely granular interior. 



The evidence thus points to orthoid affinities for 

 Eostrophomena rather than to strophomenoid ones. 

 It is not known if either of the shells placed here had 

 a deltidium or chilidium, but even if such were present 

 they would in themselves not prove this early presence 

 of strophomenoids. 



Subfamily HESPERORTHIN^ Schuchert and 

 Cooper 1931 



Progressive Orthidas characterized by a long and 

 wide ventral interarea, subreniform ovarian impressions 

 separated by subparallel pallial sinuses, and a low 

 median ridge. The brachiophores are long and more 

 advanced than in the Orthinje. Remnants of the 

 primitive deltidium and chilidium are retained in a few 

 forms. Marginal growths on the sides of the open del- 

 thyrium are conspicuous and such occur as well in 

 shells having a deltidium. 



The subfamily may have arisen in the Eoorthida: 

 and contains the genera Hesperorthis Schuchert and 

 Cooper, Schfzoramma Foerste, and Dolerorthis Schu- 

 chert and Cooper. 



Genus HESPERORTHIS Schuchert and 

 Cooper 1931 



(Gr. hesferos, West) 



PI. 4, figs. 13, 14, 17-27, 29; pi. 29, fig. 3 



Orthis (pars) Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 



1892, pp. 192-194, pi. 5, figs. 5-14. 

 Hesperorthis Schuchert and Cooper, Amer. Jour. Sci. (5), 



vol. 22, 1931, p. 244. 



