PLATE XCIII. 309 
Protrortuis winet Walcott (p. 743). 
Figure 5. Distorted cast of interior of ventral valve. U.S. Nat. Mus. Cat. No. 52437a. 
5a. Distorted ventral valve, the type specimen, compressed in argillaceous shale. U.S. Nat. Mus. Cat. No. 
52437b. 
5b and 5c. Casts of distorted dorsal valves. U.S. Nat. Mus. Cat. Nos. 52437c and 52437d, respectively. 
The specimens represented are all from Locality 28, Upper Cambrian shales about 100 feet above the Olenellus 
horizon south of Highgate Falls, 0.25 mile (0.4 km.) east of Swanton, Franklin County, Vermont. 
Nisusia (JAMESELLA) NAUTES (Walcott) (p. 734). 
Figures 6 and 6a. Exterior of ventral valves compressed and distorted in argillaceous shale of Locality 163, Middle 
Cambrian Spence shale member of the Ute limestone in Spence Gulch, 15 miles (24.2 km.) west of 
Montpelier, Bear Lake County, Idaho. U.S. Nat. Mus. Cat. Nos. 52432a and 52432b, respectively. 
Figure 6 represents the type specimen. ; 
6b. Interior of dorsal valve associated with specimens represented by figures 6 and 6a. U.S. Nat. Mus. Cat. 
No. 52482c. 
Nisusta (JAMESELLA) SPENCEI (Walcott) (p. 737). 
[Text fig. 62, p. 737.) 
Fiaure 7. Compressed ventral valve, from Locality 11q, Middle Cambrian limestone in Ic of the Marjum limestone, 
in ridge east of Wheeler Amphitheater, House Range, Utah. U.S. Nat. Mus. Cat. No. 52436a. 
7a. Compressed ventral valve, from Locality 163, Middle Cambrian Spence shale member of the Ute limestone 
in Spence Gulch, 15 miles (24.2 km.) west of Montpelier, Bear Lake County, Idaho. U.S. Nat. Mus. 
Cat. No. 52485b. This is the type specimen. 
