BILLINGSELLIDiE. 731 



study the actual specimens, I think it best to refer the species to Nisusia. "Orthis vaticina" 

 was a manuscript name given by Salter to shells subsequently referred to " Orthis lenticularis ' ' by 

 Davidson [1869, p. 231]. 



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

 the Parcdoxides zone, near Adrados, north of Sabero and Bofiar, Cantabrian Mountains, Province of Leon, northwestern 

 Spain. 



JAME SELLA Walcott,o subgenus of NISTJSIA. 



Nisusia (Jamesella) Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 252. (Characterized as below as a new subgenus.) 

 Nisusia (Jamesella) Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PL XI, and pp. 142 and 147. (Classifica- 

 tion of genus.) 



There are several species of Lower Cambrian brachiopods that differ from Nisusia festinata 

 in the absence of the strong spines on the radiating ribs. This character is so marked that I 

 separate the species without it as a subgeneric group. 



Type. — Orthis perpasta Pompeckj. 



The subgeneric name is in memory of Dr. Joseph F. James, a paleontologist who assisted 

 me in tlie preparation of material for the study of the OleneUus fauna. 



Nisusia (Jamesella) amii Walcott. 



■^ Plate CI, figures 6, 6a-b. 



Nisusia (Jamesella) amii Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 252. (Described and discussed as below as 

 a new species.) 



Ventral valve convex, elevated at the umbo, with the beak slightly incurved; area high, 

 vertical, slightly incurved; delthyrium triangular, higher than its greatest width and covered 

 by a convex deltidium, wMch is imperforate. Surface of shell marked by numerous fine, 

 rounded, equidistinct ribs that increase by interpolation; about 8 ribs in a distance of 2 mm. 

 at frontal margin. Size: Length, 8 mm.; width, 10 mm.; elevation at umbo, 4 mm. 



The front margin of the deltidium is broken so that it is impossible to state whether it 

 was arched as is the deltidium of Nisusia festinata (Billings). There is no trace of a foraminal 

 aperture in the deltidium. The fine, regular ribs and high area serve to distinguish this from 

 other species of the genus. Dorsal valve unknown. 



The specific name was given in honor of Dr. H. M. Ami. 



Formation and locality. — Lower Cambrian: (56a) A limestone bowlder in the Sillery conglomerate, on the 

 south shore of St. Lawrence River 4 miles (6.4 km.) below Quebec, Canada. 



Nisusia (Jamesella) argenta Walcott. 



Plate CI, figures 9, 9a-b. 



Nisusia (Jamesella) argenta Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 252. (Described and discussed somewhat 

 as below as a new species.) 



The outline of the ventral valve is subrect angular, with the hinge line a little shorter than 

 the greatest- width. Strongly convex with a keel-hke median elevation extending from the 

 incurved beak over the elevated umbo to the front margin, with gradually increasing width. 

 Area low, with the minute beak curving down to and possibly slightly over it. 



Dorsal valve depressed, convex, with a rather strong median fold (PL CI, fig. 9b); area 

 unknown. 



<2 The synonymy for this subgenus does not give a complete record of the various genera under which the species now included in Jamesella 

 -were formerly placed; it gives only those references in which the genus is discussed or described. To complete the record the following mere generic 

 xeferences are listed: 



Orthis Feistmantel. 

 Orthis Jahn. 

 Orthis Katzer. 

 Orthis Krejci. 

 Orthis Eusta. 



Orthis Novak. 



Orthis Wentzel. 



Orthisina de Verneuil and Barrande [ISeO, p. 536]. 



Orthis Pompeckj [lS96b, p. 514, 515, and 516]. 



Protorthis Walcott [1905a, pp. 283 and 285]. 



