BILLINGSELLID^. 785 



ridge; lateral branches extend from the main sinus toward the sides; the impressions of the 

 anterior and posterior adductor muscle scars occm- on the slopes of the median ridge and the 

 oval depressions; somewhat obscure radiatmg liaes mark the anterior portions of the siarface. 



Observations. — This shell is distinguished by its strongly marked median ridge on the 

 ventral valve and sinus on the dorsal valve. In general form and surface markings it is not 

 unhke 'Eoorthis desmopleura (Meek) and E. wichitaensis (Walcott). 



The specific name is derived from Pagoda Hill, the type locality. 



Formation and locality. — Upper Cambrian: (C56) Lower part of Chaumitien limestone, at Pagoda Hill [Black- 

 welder, 1907a, p. 4S (part of last list of fossils)], 1 mile (1.6 km.) west of Tsinan; and (C64) lower part of the 

 Chaumitien limestone [Blackwelder, 1907a, p. 42 (part of last list of fossils)], 0.66 mile (1.1 km.) west of Tsinan; 

 both in Shantung, China. 



Eoorthis papias (Walcott). 



Plate XCI, figure 4. 



Orthis (Plectorthis) papias Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 268. (Characterized as below as a new 

 species.) 



This species is fomaded to receive a form represented by two small dorsal valves from the 

 Paradoxides zone of Newfoundland. They are moderately convex, with a low area divided by 

 a broad delthjrrium; surface marked by numerous, rounded, depressed ribs, crossed by con- 

 centric striae and ridges of growth. Length of shell, 4 mm. ; width, 5 mm. 



Formation and locality. — Middle Cambrian: (61) Shales near the top of No. 6 of the Manuels Brook section 

 ■[Walcott, 1891b, p. 261], east side of Manuels Brook, Conception Bay, Newfoundland. 



Eoorthis primordialis (de Vemeuil and Barrande). 



Plate XCVII, figures 1, la-d. 



Orthis primordialis de Verneuil and Barrande, 1860, Bull. Soc. g6ol. France, 2d ser., vol. 17, pp. 532-533, PI. 

 VIII, figs. 6, 6a-d. (Described and discussed in French, as a new species; see below for translation. Figs. 6, 

 6a-d are reproduced in this monograph, PI. XCVII, figs. 1, la-d, respectively.) 



Orthis primordialis de Verneuil and Barrande, Mallada, 1875, Bol. Com. Mapa Geologico Espana, tome 2, p. 31. (Men- 

 tioned in Spanish.) 



The origmal description by de Verneuil and Barrande follows : 



Shell transverse, rounded on the sides, wider than long. Hinge ridge does not extend to lateral extremities and 

 measures hardly more than three-fourths of the total breadth of the shell. The two valves are of about the same thick- 

 ness. The ventral valve" is provided with an area hardly higher than that of the opposite valve, but it is distinguished 

 from it by a sinus which is almost as deep as that of the Spirifers, and which in front forma a very pronounced and 

 more or less sharp fold. Surface ornamented with strite, very dichotomous on the sides and almost simple in the sinus; 

 at a distance of 5 mm. from the beak, 7 striae are counted in a space of 5 mm. 



Breadth, 16 mm.; length, 12 mm.; thickness, 7 mm. 



By its deep sinus , this species is distinguished from most of its congeners and establishes a sort of passage between 

 the genera Orthis and Spirifer; however, the pronounced area observed on each of the two valves is a characteristic 

 which links it with the former rather than with the latter genus. Orthis species provided with sinuses are rather rare; 

 the principal ones are 0. sinuata Hall and 0. striatula Schl., which for that matter have no other analogy with our 

 species. It might perhaps be assimilated to 0. lynx, which also has two areas equally developed, but the latter species 

 will always be recognized by the small number and nondichotomous nature of its folds. 



Observations. — This shell is more strongly developed in the sinus of the ventral valve and 

 the fold of the dorsal valve than any other species of Cambrian Eoorthis, with the possible excep- 

 tion of E. indianola (Walcott) of the IVIiddle and Upper Cambrian of the Wicliita Mountains of the 

 United States. The latter has a higher area on the ventral valve and the sinus is often shallow, 

 while the fold is usually absent. 



Formation and locality. — Middle Cambrian; (350 [de Vemeuil and Barrande, 1860, p. 538]) Red limestone of 

 the Paradoxides zone, near Adrados, north of Sabero and Bofiar, Cantabrian Mountains, Province of Leon, north- 

 western Spain. 



a Following here the e.\aniple of Owen and Davidson, we call ventral valve the larger of the two, the one which is provided with a large area, 

 and which formerly was called dorsal valve. 



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