772 CAMBRIAN BRACHIOPODA. 



Ohservations. — Waagen [1891, p. 102] describes this shell at length and also gives a num- 

 ber of illustrations that are more or less diagrammatic. Through the courtesy of Doctor 

 Holland, the director of the Geological Survey of India, I have been able to study the type 

 specimens. I can not see as much in them as Waagen did, but as far as my observations go 

 they agree with his, except that the characters shown on the specimen represented by his 

 figure 15 [1891, PI. I] and figure 1 [1891, PI. II] appear to me to be the result of fracture caused 

 by compression of the original shell and not to be muscle scars, etc., as interpreted by Waagen 

 [1891, Pis. I and II]. 



The differences between this shell and the nearest known forms are mentioned under the 

 description of the genus (see p. 771). 



The specific name is given in honor of Dr. H. Warth, of the Geological Survey of India. 



Formation and locality. — Uiddle Cambrian: (357d [Waagen, 1891, p. 104]) "Concretionary shales of the 

 Khussak group" at several localities between Chel Hill and Kiura (Khewra), eastern part of Salt Range, India. 



Subfamily EOORTHINJE Walcott. 



Genus EOOBTHIS Walcott. o 



l^ivc, dawn; and 6p6dc, straight.] 



Not Plectorthis Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 194-195. (Characterized 



as a new genus; see below for copy. This genus, as now restricted, is not known to occur in the Cambrian.) 

 Orthis {Plectorthis) Walcott [not (Hall and Clarke)], 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 257-259. (Original 



characterization copied and genus discussed somewhat as below.) 

 Plectorthis Grabau and Shimer (in part) [not Hall and Clarke], 1907, North American Index Fossils, vol. 1, pp. 



250 and 251. (Characterized. Includes both true Plectorthis and Eoorthis.) 

 Eoorthis Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, pp. 102-104. (Described and discussed as below 



as a new genus.) 

 Eoorthis Walcott, 1908, idem, vol. 53, No. 4, PL XI, and pp. 142 and 148. (Classification of genus.) 



In their subdivision of the genus Orthis Dalman, Hall and Clarke [1892c, p. 192] restricted 

 the genus Orthis to the group of which Orthis callactis Dalman is the type, and, among American 

 forms, Orthis tricenaria of the Trenton and Hudson faunas. These forms show the existence 

 of a transverse apical plate in the delthyrium of the ventral valve. The name Plectorthis 

 was proposed for a second group, of which Orthis 'plicateUa was made the type (PL XCVI, figs. 

 4, 4a), and of this the authors [1892c, p. 194] say: 



This is a persistent form, which in American faunas, so far as known, is limited to the Trenton and Hudson River 

 formations. \^1iile it retains the strong external ribs of the typical Orthis. these are not invariably simple (0. jissicosta 

 Hall; 0. triplicatella Meek; 0. xquivalvis Hall [not Davidson]; 0. jamesi, Hall) (PL XCVI, figs. 5, 5a-c). The cardinal 

 area of the pedicle valve is comparatively low and the valves are subequally convex. In the interior, the character 

 of the muscle scars, dental lamellse and cardinal process is essentially the same as in group I (Orthis), and the minute 

 structure of the shell appears to be in precise agreement with that of 0. calligramma though no evidence of tubulose 

 costee has been observed. In Orthis jamesi, which is placed in this association, there is occasionally a deviation toward 

 the resupinate contour exemplified in group IV (Orthis subquadrata) and group V (Orthis sinuata). 



In the Cambrian faunas I find a group of species intermediate between the typical forms 

 of Billingsella and of Orthis, as limited by Hall and Clarke [1892c, p. 193], which I have referred 

 for a long time to Hall and Clarke's Plectorthis, placing that genus as a subgenus of Orthis. 



a The synonymy for this genus does not give a complete record of the various genera under which the species now included in Eoorthis were 

 formerly placed; it gives only those references in which the genus is discussed or described. To complete the record for the species taken up in 

 this monograph the following mere generic references are listed: 



Orthis de Verneuil and Bnrrande [1860, p. 532]. 



Orthis Kjerulf [ISeS, p. 1]. 



Orthis Barrande [ISOSa, p. 99; 18S8b, p. C90]. 



Orthis Meek [1870, p. 425; 1872, p. 295]. 



Orthis Mallada [1875, p. 31]. 



Orthis Kayser [1876, p. 8]. 



Orthis Reraele [1881, p. 69]. 



Orthis Brogger [1882, p. 48]. 



Orthis Kayser [1883, p. 34]. 



Orthis Eemele [1885, p. 6]. 



Orthis Roemer [1885, pp. 36, 37, and 38]. 



Orthis Winchell [18S6, p. 317]. 



Orthis Gagel [1890, pp. 10 and 34]. 



Orthisina? Matthew [1892, p. 49]. 



Strophomena Matthew [1893, p. 102]. 



Orthis Pompeckj [189ea, p. 4; 1896b, p. 514]. 



Rafinesquinaf Schuchert [1897, p. 338]. 



Orthis Kayser [1897, p. 280]. 



OrtAwf Walcott [1899, p. 451]. 



Orthis Pompeckj [1902, p. 7]. 



Orthis Weller [1903, p. 113]. 



Orthis ? Etheridge [1905, p. 249]. 



Orthis (Plectorthis) Walcott [1906, p. 570]. 



Orthis (Plectorthis) Moberg and Segerberg [1906, p. G9]. 



Nisusia Walcott [1908d, p. 97] (by mistake). 



