246 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvni. 



BILLINGSELLA WHITFIELDI Walcott. 



Kulorgind whitfidili Waiaott, INIong. U. S. Geol. Sur., \'1II, 1884, p. 18, \A. ix, 



fifj;s. 4, 4a. 

 Bil/hKjscllo whiljiddi SrnucHERT, Bull. U. >S. Geol. Sur. No. 87, 1897, \). 159. 



Shell convex, hinge line straight and a little less than the greatest 

 width of the shell, sides rounding regularly into the slightly convex 

 frontal margin. 



Ventral valve quite convex, elevated along the center to form a flat 

 depressed fold, and sloping quite rapidly from this to the lateral and 

 cardinal margins; median elevation with about five rather faintly 

 defined, simple plications, that reach up to the higher portion of the 

 valve; beak small, a little depressed, and rising alwve the area; cardinal 

 margins straight and diverging from the beak at an obtuse angle; 

 character of area unknown. 



Dorsal valve depressed convex, with a rather wide, shallow, median 

 depression, and two short plications on each side of it toward the 

 front, which are obsolete in some of the specimens; the area between 

 the cardinal edges and the elevation of the sides of the mesial depres- 

 sion is depressed and corresponds to the flattened lateral slope of the 

 ventral valve. 



Surface marked by fine, very clearly defined concentric stride that 

 are crowded together into narrow ridges and are subparallel to the 

 front and lateral margins of the shell. 



I>. wh/tjleldi belongs with the group of species including B. sale- 

 wte7isis or shells with coarse plications and very fine concentric stride. 

 The latter species occurs with the Olenellus fauna in eastern New York, 

 and B. whitfieldl in the Middle Cambrian of Central Nevada. 



Formation and locality. — Lower Cambrian. Prospect Mountain 

 group, beneath the Secret Canyon shah?, on the west side of Secret 

 Canyon, Eureka District, Nevada. 



OTUSIA, new subgenus of BILLINGSELLA. 



This name is proposed to include Ort/ds sandhergl of N. H. Winchell, 

 which is the only species known at present. The subgeneric and spe- 

 cies characters are included in the description of the species, 



BILLINGSELLA (OTUSIA) SANDBERGI Winchell. 



Ortliis sandhergi N. H. Winchell, Fourteenth Ann. Rep. Geol. Nat. Hist. Sur. 



Minnesota, 1886, p. 318, pi. ii, figs. 8, 9. 

 Orthis f sandhergl Walcott, INIong. XXXII, U. S. Geol. Sur., 1899, p. 452, pi. 



Lxi, figs. 2, 2a-(l. 



Shell small, transverse, subquadrate in outline, exclusive of the 

 acute cardinal extremities. Valves slightly convex, with a straight 

 hinge line longer than the greatest width of the shell; cardinal area 

 narrow but well developed on each valve and divided by a rather large 

 open delthyrium. 



