342 



CAMBRIAN BRACHIOPODA. 



feet (884 m.) above the Lower Cambrian and 1,500 feet (457.2 m.) below the Upper Cambrian in the central part of 

 the bed forming la of the Marjum limestone [Walcott, 1908f, p. 179], about one mile (1.6 km.) south-southwest of Mar jum 

 Pass; all in the House Range [Walcott, 1908f, PL XIII], Millard County, Utah. 



(lis) Shales just above Simpson Spring, about 20 miles (32.2 km. ) west-southwest of Vernon, on the stage road from 

 Vernon to Fish Spring, Tooele County, Utah. 



(lOw) Shaly limestones about 5 miles (8 km.) northeast of Osceola, on the east side of the Snake Range, ^Vhite 

 Pine County; and (58) shaly limestones in upper beds of Secret Canyon shale, either in New York or Secret Canyon, 

 Eureka district [Hague, 1892, Atlas], Eiu:eka County; both in Nevada. 



Specimens that are compared with Micromitra sculptilis occur at the following locality: 



Middle Cambrian: (54i) About 2,950 feet (899.2 m.) above the Brigham quartzite and 1,225 feet (373.4 m.) below 

 the Upper Cambrian in the limestone forming le of the Bloomington formation [Walcott, 1908f, p. 194], in Blacksmith 

 Pork Canyon, about 10 miles (16.1 km.) east of Hyrum, Cache County, Utah. 



Micromitra sculptilis endlichi Walcott. 



Text figure 22. 



Micromitra sculptilis endlichi Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 56. (Characterized as below 

 as a new variety.) 



This form is represented by a single specimen of a ventral valve. The surface is similar 

 to that of Micromitra sculptilis (Meek), but the valve is more elongate, 

 less elevated, and larger (5 mm. in diameter) than the specimens of 

 the latter from the type locality. 



The varietal name is given for ]\Ir. F. M. Endlich of the Ha5^den 

 Survey. 



Formation and locality. — Upper Cambrian: (8o) Limestone 2 miles (3.2 km.) 

 north of Aurum, Schell Creek Range, White Pine County, Nevada. 



Micromitra zenobia n. sp. 



Figure 22. — Micromitra sculptilis 

 endlichi Walcott. A, A', Top 

 and side views of tlie type speci- 

 men, a ventral valve from Local- 

 ity 8o, Upper Cambrian lime- 

 stones, 2 miles (3.2 km.) north of 

 Aurum, White Pine County, 

 Nevada (U. S. Nat. Mus. Cat. 

 No. 5149S). 



Text figure 23. 



Most of the specimens of this species are flattened in the shale, 

 but both valves aj^pear to have been moderately and nearly equalty 

 convex. The beak of the ventral valve is slightly in advance of the 

 posterior margin and incurves slightly over a well-defined cardinal 

 slope which is nearly straight and almost as wide as the greatest diam- 

 eter of the shell. The pseudodeltidium is moderately convex and apparently extends about 



half the distance from the beak to the posterior margin. 



Growth lines are fairly coarse and regular. In the ventral valve they bend abruptly at 



the cardinal slope, on which they are very fine and very irregular. In 



other words, the cardinal slope is well defined and is covered with an 



irregular confusion of minute ridges which seem to bear little relation 



to the concentric ridges on the surface of the shell. This pattern can 



not be seen on the pseudodeltidium. 



In some of the adult shells from the type locality (35k) a faint 



radial crenulation can be seen near the apex. Fragments of lime- 

 stone (Locality 57c) contain many small shells, probably the young, 



with radial folds and a crenulation of the concentric strife similar to 



that in Micromitra sculptilis. The crenulations have been observed 



in one perfectly preserved adult specimen. The specimens from the 



limestone may be distinct. 



FoKMATiON AND LOCALITY. — Middle Cambrian: (36k) Burgess shale member of the 

 Stephen formation, west slope of ridge between Mount Field and Wapta Peak, 1 mile 



{1.6 km.) northeast of Burgess Pass, above Field; and (58 1) about 1,830 feet (557.8 m.) above the Lower Cambrian in 

 the limestone forming 3b of the Stephen formation [Walcott, 1908c, p. 238 (7)], on the east side of Mount Stephen 

 about 3,000 feet (914.4 m.) above the Canadian Pacific Railway track 3.5 miles (5.6 km.) east of Field; both in British 

 Columbia. 



Figure 23.— Micromitra zenobia n. 

 sp. Top view of type specimen, a 

 ventral valve from Locality 36k, 

 Middle Cambrian Stephen forma- 

 tion 1 mile Cl-6 km.) northeast ol 

 Burgess Pass, above Field, British 

 Columbia (U. S. Nat. Mus. Cat. 

 No. 58311H, 



