380 CAMBKIAN BEACHIOPODA. 



The species of the genus and its subgenera recognized by Mickwitz [1896] in Russia are: 



Obolus (Acritis) antiquissimus (Eichwald). 

 Obolus (Euobolus) : 



apollinis Eichwald. 



apoUinis ingricus (Eichwald). 



apollinis maximus Mickwitz. 



apollinis quenstedti (Mickwitz). , 



eichwaldi Mickwitz. 



elegans Mickwitz. 



panderi Mickwitz. 



schmidti Mickwitz. 



triangularis Mickwitz. 



triangularis inornatus Mickwitz. 



volborthi Mickwitz. 

 Obolus (Leptembolon) lingulseformis Mickwitz. 

 Obolus (Mickwitzella) siluricus (Eichwald). 



Obolus (Schmidtia): 



acuminatus Mickwitz. 



acuminatus alatus Mickwitz. 



acuminatus humeratus Mickwitz. 



acuminatus subtriangularis Mickwitz. 



celatus (Volborth). 



celatus orbiculatus Mickwitz. 



celatus praecisus Mickwitz. 



crassus Mickwitz. 



crassus angulatus Mickwitz. 



obtusus Mickwitz. 



obtusus acutus Mickwitz. 



obtusus ellipticus Mickwitz. 



obtusus extenuatus Mickwitz. 



obtusus latus Mickwitz. 



obtusus longus Mickwitz. 



obtusus minutus Mickwitz. 



Obolus acadicus Walcott. 



^ Plate XI, figure 5. 



Obolus acadica Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 324-325. (Characterized and discussed as below as 

 a new species.) 



Only interiors of the dorsal valve of this species occur in the collections made by Loper 

 on McNeil Brook in 1900. The material was provisionally referred to LinguleUa concinna 

 Matthew, but the broadly rounded subquadrilateral form of the dorsal valve seems to 

 distinguish it from that species and also from Oholus (Palseoholus) hretonensis (Matthew). 



The visceral area is narrow, extending a little in advance of the center of the valve. The 

 main vascular trunks are narrow and widely separated. They belong to the submarginal group 

 and are thus quite unlike those of 0. (P.) hretonensis. ^ The exterior surface and ventral valve 

 are unknown. 



The specific name is derived from Acadia, the original name for Nova Scotia, in which the 

 species occurs. 



Formation and locality. — Upper Cambrian : (3h) Shale and phaly limestone on McNeil Brook, 1.5 miles (2.4 km.) 

 east ot Marion Bridge, eastern Cape Breton, Nova Scotia. 



Obolus? advenus Barrande. 



i/ 

 I Plate XII, figures 5, 5a-b. 



Obolus f advena Barrande, 1879, Systeme silurien du centre de la Boheme, vol. 5, pt. 1, PI. XCV, figs, iv: 1-2. (No 

 text reference. Figs. 2A, lA, and 2B are copied in this monograph, PL XII, figs. 5, 5a-b, respectively.) 



This species is known to me only by the figures of Barrande [1879b, PI. XCV, fig. iv] some 

 of which are copied on Plate XII. The species is of the same type as 0. com'plexus Barrande, 

 so far as the means of comparison permit us to judge. It occurs at the same relative geologic 

 horizon as 0. complexus. 



Formation and locality. — Lower Ordovician: (303d [Barrande, 1879b, PL XCV]) Etage dl, Swarow, Bohemia, 

 Austria-Hungary . 



, / Obolus anceps Walcott. 



Plate X, figures 3, 3a-f. 



Obolus anceps Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, pp. 388-389. (Described and discussed as below as a 

 new species.) 



General form broadly ovate, somewhat subcuneate.- Valves moderately convex. Surface 

 marked by fine lines of growth, and finer slightly undulating concentric striae; when the outer 

 layer is exfoliated the outer surface of the inner layer is marked by very fine, radiating striae 

 and numerous lines of growth; the inner surface of the shell is nearly smooth, judging from a 



