CAMBRIAN BRACHIOPODA WALCOTT 9I 



the Upper Cambrian in the House Range Section. It differs from 

 L. nitens (see below), which occurs a short distance above it in the 

 section, and with which it is also associated, in having a less elevated 

 ventral valve and a less convex dorsal valve, and from L. transversa 

 (see p. 92) in being more rounded in outline and less convex. It 

 appears to be more nearly related in form to L. miiiuta (Hall and 

 Whitfield) [1877, p. 206] ; it differs, however, materially in the 

 ■character of the interior markings of the ventral valve, features 

 which also separate it from L. girtyi Walcott [1902, p. 602] and 

 L. tennesseeiisis Walcott [1902, p. 604]. 



Formation and Locality. — Upper Cambrian: 1,160 feet (353-6 

 m.) above the Middle Cambrian and 2,155 feet (656.8 m.) below 

 the top of the Upper Cambrian, in the arenaceous shales and lime- 

 stones of the Orr formation [Walcott, 1908a, p. 10], 4 miles (6.44 

 km.) south of Marjum Pass, House Range, Millard County, Utah. 



LINNARSSONELLA NITENS, new species 



Plate 9, Figure; 7 



The outline of the valves and the exterior appearance of this shell 

 are much like those of Linnarssonella modesta (see p. 90) . It differs 

 in having on the ventral valve a low, distinct area, with the per- 

 forated apex directed backward on nearly the same plane as the 

 umbo, or most elevated portion of the valve. The dorsal valve is 

 more convex and its interior has a strong median ridge extending 

 forward from the posterior margin about two-thirds of the distance 

 to the front margin, a feature but little developed in L. modesta. 

 From L. minuta (Hall and Whitfield) [1877, p. 206] it differs in 

 the higher apex of the ventral valve, and from L. transversa (see p. 

 92) in the latter character and in the more circular outline of the 

 aperture of the valves. 



A single specimen of L. modesta was found associated with this 

 species. 



In size L. nitens varies from 1.5 to 2 mm. in diameter. 



Formation and Locality. — Upper Cambrian: (i) 1,160 feet 

 (353-6 m.) above the Middle Cambrian and 2,133 feet (636.8 m.) 

 belozv the top of the Upper Cambrian, in the arenaeeous shales and 

 limestones of the Orr formation [Walcott, 1908a, p. loj, 4 miles 

 (6.44 km.) south of Marjum Pass, House Range, Millard County, 

 Utah. (2) About 2,575 feet (784.9 m.) above the top of the Cam- 

 brian quartzitic sandstones, in a blue limestone about 2 miles (3.22 

 km.) southeast of Muskrat Spring, on the northwest face of Grants - 

 ville Peak, Stansbury Range, Tooele County, Utah. 



