GENER.A OF THE SUBORDER ORTHOIDEA 



51 



genus as strictly smooth Billingscllid.T has little generic 

 value. However, the name will be useful for the 

 oldest Eoorthid.T, having finely costellatc shells with 

 interiors that approach the features of Billingsrlla. 



Discussion. — In choosing Wimanclla simplex as 

 the genotype, Walcott unfortunately selected an almost 

 characterless shell. The material from Montana oc- 

 curs in a soft shale, and since the forms are rather 

 thin-shelled they are b.adly crushed and show little of 

 the morphology. This is particularly true of the type 

 specimen (see pi. 89, fig. 2 of Walcott 1912). The 

 most important clue to the ventral morphology of these 

 shells is furnished by a specimen referred to W. simplex 

 (Ibid., pi. 89, fig. 2d), in which the ventral muscula- 

 ture consists of two large diductor tracks, closely adja- 

 cent at the posterior of the shell but divergent at the 

 front. In the space between the antero-median mar- 

 gin of the diductor tracks is a low suboval elevation 

 corresponding probably to the adductor impressions. 

 This is exactly the same musculature as shown by the 

 type of Bilitngsclla htghlatiAensts (see Ibid., pi. 87, fig. 

 4b). Here the adductor impression is not shown be- 

 tween the diductors but is actually present in the speci- 

 men from which the figure was drawn. This species 

 also has prominent ventral pallial trunks as in BUllngs- 

 elloy is likewise very finely ribbed, and seems to cor- 

 respond well with the concept of Wlmanella described 

 in this paper. 



Wlmanella horealls Walcott is another finely costel- 

 late species and this one too is said to have faint pallial 

 marks, although they do not show on Walcott's fig- 

 ures (1924, pi. Ill, fig. 2). The writers have ex- 

 cluded Wlmanella harlanensls (Wale.) from this 

 genus, since its structure, especially in the musculature 

 of the two valves, relates it to Syntrophla and Clark- 

 ella. The placing of Wlmanella tnyoensls Walcott 

 among the articulate brachiopods is questionable. 



Genus EOORTHIS Walcott 1908 



PI. 1, figs. 23, 26, 28 



Walcott, Smiths. Misc. Coll., vol. 53, 1908, p. 102; Camb. 

 Brach., 1912, p. 772, pi. 91, figs. 1-ls, pi. 92, figs. 

 2-2d, 3-3e, t. fig. 7. 



Genoholotype. — Orthls remnlchaW'mzhcW 1886, 

 Geol. Surv. Minn., 14th Ann. Rept., pp. 317-318, 

 pi. 2, fig. 7. 



Description. Exterior. — Shell subquadrate to 

 transversely subelliptical ; hinge-line straight, cardinal 

 extremities usually obtusely angular; lateral profile 

 subequally biconvex; anterior commissure sulcate; 

 dorsal sulcus marked most clearly on the middle and 

 dorsal part of the valve; ventral interarea broad, 

 slightly curved, apsacline; delthyrium wide and not 

 covered by a deltidium. Dorsal interarea short, ana- 

 cline; notothyrium wide, not closed by a chilid- 

 ium. Surface multi- to fascicostellate. Test fibrous, 

 impunctate. 



Ventral Interior. — Delthyrial cavity shallow; teeth 

 strong; dental plates strong, receding, continued 

 around the lateral margins of the muscle field as a 

 low ridge. Musculature orthoid, diductor scars tri- 

 angular, adductor track median, expanding in front. 



Dorsal Interior. — Notothyrial cavity shallow ; brach- 

 iophores consisting of flattened oblique plates attached 

 to the roof of the valve on the surface of which the 

 interarea rests, the whole forming the walls of the 

 notothyrial cavity. The sockets are narrow and shal- 

 low (see pi. 1, figs. 23, 28). Notothyrial platform 

 of adventitious shell crowded under the brachiophores 

 to support them; cardinal process a simple ridge ex- 

 panded toward the front. Median ridge wide and 

 strong. 



Geological range. — Upper Cambrian to Ozark- 

 ian of North America. 



Species 



Eoorthis in<lianola (Walcott) 1905 

 E. sulcata (Walcott) 1905 

 E. texana Walcott 1905 

 E.u'khitaetisis iyfiXcon) 190 5 

 E. u'infieUensis (Walcott) 1905 

 Orlhis remnicha Winchell 1886 



? Efjorlhis diablo (Walcott) 1905 



? E. faicigera Walcott 1924 



? E.nympha Walcott 1905 



? E.ochus Walcott 1924 



? Orlhis desmopleura Meek 1872 



Distinguishing characters. — The generic char- 

 acters of Eoorthis are: multicostate to multicostcllate 

 exterior, open delth) rium, receding dental plates; open 

 notothyrium; billingselloid crural apparatus and rudi- 

 mentary cardinal process. 



Composition of the genus. — Before the genus 

 Eoorthis was erected by Walcott in 1908 he referred 

 the species to Plectorthls, a stock common in the Mid- 

 dle Ordovician. In 1912, when he published his 

 monumental work on Cambrian brachiopods, Walcott 

 made a virtual dump box of Eoorthis, referring to it 

 no fewer than 33 species believed to have more or less 

 of the external expression of the genotype, Orthls rem- 

 nicha, but in most of them the interior is unfortunately 

 unknown. Of these 33 species, 19 occur in North 

 America, and after a restudy of all the species we are 

 unable to place even generically no fewer than 18. 

 Nine species (3 doubtful) we leave with Eoorthis, and 

 refer 1 each doubtfully to Protorthls and Flnkelnhurgla, 

 2 to Orusla and 5 to Archteorthls. This then leaves 

 unplaced 6 species in America, 6 in China, 1 in 

 Europe, and 1 each in Australia and Argentina. 



Discussion. — The ventral interior of Eoorthis 

 remnicha is distinctive, as it has structural parts that 

 ally it with Hesperorthls or Orthls, and with the an- 

 cestral stock, Bllllngsella. The teeth are strong and 



