466 CAMBRIAN BRACHIOPODA. 



of the genus except 0. (T7.) aurora, from which it differs in having a more elongate form and in 

 the fact that the surface markings, though of the same type, vary in being much coarser and 

 in having longer undulations. (Compare PL XXVIII, fig. 2d, with PI. XL VI, fig. Ih.) 



The form found by Stuart Weller [1900, p. 112] in the Upper Cambrian sandstones of north- 

 ern New Jersey is illustrated on Plate XLIX, figures 2, 2a. 



The specific name was given for Mr. R. E. Stone [Whitfield, 1882, p. 345]. 



FoKMATioN AND LOCALITY. — ^TJpper Cambrian: (85x) Upper beds of the "St. Croix sandstone" at Mazomanie, 

 Dane County; (81b) "St. Croix sandstone" near Devils Lake, Sauk County; (328m) sandstone 1 mile (1.6 km.) south 

 of Osceola, Polk County; (328f [Hall, 1863, p. 128]) sandstone at the falls of St. Croix River, Polk County; and (85 and 

 85s) « "St. Croix sandstone" at Prairie du Sac, Sauk County; all in Wisconsin. 



(lie) Hardyston quartzite [Weller, 1903, pp. 110 and 112], O'Donnell and McManniman's quarry, Newton, Sussex 

 County, New Jersey. 



(327) Arenaceous limestone east of Gold Camp; (327a) arenaceous limestone about 500 feet (152 m.) above the base 

 of the Cambrian in McKinley Canyon; (327b) arenaceous limestone near the base of the section on the south side of 

 Cerro Cuchillo ; and (327c) arenaceous limestone in the Caballos Mountains (exact locality unknown) ; all in the Caballos 

 Mountains, Sierra County, New Mexico. 



Obolus (Westonia) THEMIS Walcott. 



Plate XI, figures 2, 2a-c. 



Obolus (Westonia) themis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 336-337. (Described and discussed as 

 below as a new species.) 



General form subsemicircular, with the ventral valve subacuminate and the dorsal valve 

 broadly ovate in outline. Valves rather strongly convex. Surface of the shell marked by 

 strong concentric lines of growth with finer intermediate striae; in addition there are very fine, 

 irregular, raised, more or less transverse strife that inosculate, forming a minutely papillose 

 or granular surface much like that of Oholus (Westonia) ella (PI. XL VII). It often occurs 

 that the outer surface has been removed by attrition in the sand, so that the shell has a smooth 

 polished surface. Owing to the condition of preservation the markings of the inner layers are 

 not preserved. The shell is strong and tliick in advance of the center. It is made up of the 

 thin outer surface layer and several inner layers or lamellae that in the posterior portions are 

 slightly oblique to the outer surface. After the shell has attained a size of 2 or 3 mm. the 

 lamellae are more oblique to the outer surface and form a thick, strong shell, the outer edges 

 of which often produce a rather rough surface. This is shown by the figures illustrating the 

 species. 



The largest ventral valve in the collection lias a length and breadth of 10 mm.; a dorsal 

 valve 10 mm. in length has a width of 11 mm. The only interior portions of the shell known 

 are on a fragmentary ventral valve in which the visceral area does not reach the center, and the 

 naain vascular sinuses are about halfway between the center and the lateral margins of the 

 valve. 



Ohservatiojis. — The general form of the shell is much like that of Obolus loperi (PI. IX) . 

 It differs from the latter in surface characters. 



Formation and locality. — Middle Cambrian: (17c) Sandy limestone 235 feet (71.6 m.) above the "Tonto" sand- 

 stone. Grand View trail, north of Last Chance copper mine, south side of the Grand Canyon of the Colorado, Arizona. 



Obolus (Westonia) wasatchensis Walcott. 



Text figures 41A-F, page 467; Plate XLIX, figures 5, 5a. 



Obolus ( Westonia) wasatchensis Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, pp. 69-70, PI. VIII, figs. 1 and la. 

 (Discussed as below as a new species. Figs. 1 and la are copied in this monograph as figs. 41 A and 41D.) 



This species is founded on some large shells that differ from Obolus ( Westonia) ella (Hall 

 and Whitfield) (PI. XLVII) in attaining a larger size and greater proportional width and in 



o 85s is the type locality, though the specimens in the United States National Musenm to which that number is assigned were collected much 

 later than the type specimens. 



