732 CAMBEIAN BRACHIOPODA. 



Surface marked by fine, concentric striae of growth and about five sharp, elevated, radiating 

 ribs on each side of the two ribs on the median ridge of the ventral valve ; the ribs of the dorsal 

 valve are more regular in spacing and size. 



Ohservations. — This shell has such strong characters that I unhesitatingly give it a specific 

 name. The only form known to me that resembles it is N. (J.) liuthani (Pompeckj) (PL CI, 

 figs. 4, 4a-b) from Bohemia. 



Formation and locality. — Lower Cambrian: (Imand Ip) « Limestones of No. 2 of the Silver Peak gi"oup, Barrel 

 Spring section [Walcott, 1908f, p. 189], about 2. .5 miles (4 km.) south of Barrel Spring and 0.5 mile (0.8 km.) east of the 

 road, in the extreme southeast corner of the Silver Peak quadrangle (U. S. Geol. Survey), Esmeralda County, Nevada. 



NisusiA (Jamesella) eeecta Walcott. 



Plate CI, figures 5, 5a-b. 



Nisusia {Jamesella) erecta Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 253. (Described essentially as below as a 

 new species.) 



General form transversely semioval; hinge line a little shorter than the greatest width; 

 Valves subequally convex. Surface marked by strong, broad, sharply rounded ribs, three at the 

 frontal margin in a distance of 2 mm. ; the ribs appear to be simple and imbifurcated from the 

 umbo to the margin, but owing to the small size of the shell this statement may be modified by 

 discovery of other specimens. Width, 9 mm. ; length, 7 mm. from beak to front of ventral 

 valve. 



Ventral valve convex; elevated at the umbo, beak marginal. Area lugh, very slightly 

 inclined backward; delthyrium large, triangular, length and width equal; deltidium convex, 

 imperforate, and nearly covering the delthj^rium. Dorsal valve regularly convex, most elevated 

 at the umbo and curving over to the rather low area. 



This species is distinguished by its strong, regular ribs and regular convexity of the dorsal 

 valve. 



Formation and locality. — Middle Cambrian: (313g) Limestone at the south end of the Timpahute Range, 

 Groome district, near the line between Nye and Lincoln counties, Nevada. 



^^ Nisusia ? (Jame&ella ?) kanabensis Walcott. 



Nisusia? (Jamesella ?) kanabensis Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, pp. 97-98. (Described and 

 discussed as below as a new species.) 



This species is represented by a single broken interior cast of a small ventral valve that 

 has a length of 3.5 mm. ; width, about 5 mm. The cast is convex, with the base of a prominent 

 extension that filled the interior of the beak. The surface is finely papillose, which proves that 

 the interior surface was finely punctate. The casts of the ribs show them to have been rather 

 sharply rounded and to have increased by bifurcation and interjpolation ; the absence of all 

 traces of casts of spine bases on the ribs leads me to refer the species to the subgenus Jamesella. 

 Area shown only by a narrow rim on one side. The delthyrium was probably quite broad. 



The reference of tliis shell to Nisusia is based on the evidence of the presence of a prolonged 

 beak and the character of the ribs. The genus is doubtful, but I do not know of any other to- 

 which a tentative reference could be made. 



The specific name is derived from Kanab Canyon, the type locahty. 



Formation and locality. — Upper Cambrian : (75) Thin-bedded limestones just below the base of the Ordovician, 

 in the Tonto group, near the water's edge at the mouth of Kanab Canyon, Grand Canyon of the Colorado, Arizona. 



Nisusia (Jamesella) kuthani (Pompeckj). 



Plate CI, figures 4, 4a-b. 



Orthis kuthani Pompeckj, 1896, Jahrb. K.-k. geol. Reichsanstalt, Bd. 45, pp. 514-515, PI. XV, figs. 8-13. (Described 



and discussed in German as a new species; see p. 733 for translation.) 

 Orthis romingeri of the following authors: Krejci, Novak, K. Feistmantel, Kusta, Katzbr, Wentzel, and Jahn. 



a Ip is the type locality. 



