734 



CAMBRIAN BRACHIOPODA. 



The specific name is given in honor of Hon. A. P. Low, deputy head and director of the 

 Geological Survey of Canada. 



Nisusia (Jaivesella) lowi occurs at horizons 186 to 294 feet (56.7 to 89.6 m.) above the 

 horizon of Nisusia festinata (Billings) in the Mount Stephen section. 



Formation and locality. — Lower Cambrian: (58k) Just below the Middle Cambrian in limestones forming 1 of 

 the Mount Whyte formation [Walcott, 190Sc, p. 240 (9)], just above the tunnel; (58p) drift block of limestone believed 

 to have come from the limestone forming 1 of the Mount Whyte formation [Walcott, 1908c, p. 240 (9)], found near the 



FiGUEE m..— Nisusia (Jamesdla) lowi Walcott.— A, A', A", Top, side, and enlarged view (X9) of exterior surface of a partly exfoliated ventral 

 valve, the type specimen, in limestone (U. S. Nat. Mus. Cat. No. 53677a). B, B', B", Top, side, and back views of cast of the interior of a 

 ventral valve, in limestone (U. S. Nat. Mus. Cat. No. 53677b). C, View of the cast of the interior of a small dorsal valve, in limestone 

 (U. S. Nat. Mus. Cat. No. 53677c). D, A compressed dorsal valve in siliceous shale (U. S. Nat. Mus. Cat. No. 57072a). 

 The specimens represented by figures 01 A, 61B, and 61C are from Locality 58k, and that represented by 61D is from Locality 57ni, both ill 



the Lower Cambrian on Mount Stephen, British Columbia. Figure 61A is copied from Walcott [1908d, PI. VIII, flg. 14]. 



Canadian Pacific Railway just west of the tunnel; and (57m) about 50 feet (15.2 m.) below the Middle Cambrian in a 

 siliceous shale correlated with lb of the Mount Whyte formation on Mount Bosworth [Walcott, 1908f, p. 213], just above 

 the tunnel; all on the north shoulder of Mount Stephen, 3 miles (4.8 km.) east of Field, British Columbia, Canada. 



(57s) About 160 feet (49 m.) below the Middle Cambrian near the base of the gray oolitic limestone forming lb 

 of the Mount Whyte formation [Walcott, 1908f, p. 212], on Mount Bosworth, north of the Canadian Pacific Railway- 

 between Hector and Stephen, on the Continental Divide between British Columbia and Alberta, Canada. 



Nisusia (Jamesella) naxjtes ("Walcott). 

 Plate XCIII, figures 6, 6a-b. 



vol. 28, pp. 283-284. (Characterized and discussed some- 



Protorthis nautes Walcott, 1905, Proc. U. S. Nat. Mus. 

 what as below as a new species.) 



This species has the same type of punctate interior surface as N. (J.) spencei, and casts of 

 the exterior are marked by minute, closely set papillae that are casts of the punctse in the shell. 

 Traces of the shell show the same type of papillae and it is highly probable that the shell was 

 punctate. The exterior form is like that of Nisusia alberta, but in the surface ribs it differs 

 from the latter and other described species of the genus. 



A ventral valve has a length of 5 mm.; width, 8 mm. A dorsal valve, length, 7 mm.; 

 width, 10 mm. There is considerable variation in the relative proportions between length and 

 width. 



Formation and locality— Middle Cambrian : (55c and 163) " Spence shale member of the Ute limestone [Walcott, 

 1908a, p. 8], about 50 feet (15.2 m.) above the Brigham quartzite, and 2,755 feet (839.7 m.) below the Upper Cambrian, 

 in a ravine running up into Danish Flat from Mill Canyon, about 6 miles (9.6 km.) west-southwest of Liberty and 15 

 miles (24.2 km.) west of Montpelier, Bear Lake County, Idaho. 



o 163 is the type locality. 



