764 CAMBRIAN BRACHIOPODA. 



(2b) Limestone just north of Beman Park, in the northeastern part of the city of Troy; Troy quadrangle (U. S. 

 Geol. Survey), Rensselaer County; (22a) limestone in Penrhyn quarries, Middle Granville, Mettawee quadrangle 

 (U. S. Geol. Survey), "Washington County; and (367a) limestone about 0.33 mile (0.5 km.) south of John Hulett's 

 farmhouse, 3 miles (4.8 km.) west of South Granville and 4.5 miles (7.2 km.) southwest of Granville, Fort Ann quad- 

 rangle (U. S. Geol. Survey) ; all in New York. 



(338d) Limestone 1 mile (1.6 km.) south of Shushan; (21 and 37) shales and limestone 1.5 miles (2.4 km.) south 

 of Salem; (36) limestone 1 mile (1.6 hm.) south of Shushan and 3.5 miles (5.6 hm.) north-northeast of Cambridge; and (33) 

 limestone on the roadside near Rock Hill schoolhouse, near North Greenwich, about 5 miles (8 km.) northwest of Green- 

 wich; all in the Cambridge quadrangle (U. S. Geol. Survey), Washington County, New York. 



Specimens that are doubtfully referred to this species occur at the following locality, 

 the stratigraphic horizon of which is doubtful : 



Lower Cambrian: (367b) Sandstone at LansLngburg, north of Troy, Cohoes quadrangle (U. S. Geol. Survey), 

 Rensselaer County, New York. 



BiLLINGSELLA STRIATA Walcott. 



Plate LXXXVI, figures 4, 4a-c. 

 Billingsella stnata Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 245. (Characterized as below as a new species.) 



The form of the ventral valve of this species is much like that of Billingsella plicatella'. 

 It differs- in having a finely striated outer surface, and in the strong development of the main 

 vascular sinuses, and the broader deltidial cavity. The only two specimens of the dorsal 

 valve are nearly fiat. 



Formation and locality. — Middle Cambrian: (149a) Limestone at the forks of Pole Creek, above Cherry Creek 

 basin, Threeforks quadrangle (U. S. Geol. Survey), Madison County, Montana. 



Billingsella whitfieldi (Walcott). 

 Plate LXXXVI, figures 5, 5a. 



Kutorgina whitfieldi Walcott, 1884, Mon. U. S. Geol. Survey, vol. 8, pp. 18-19, PL IX, figs. 4, 4ar-b. (Described 



and discussed essentially as below as a new species. The specimens represented by figs. 4, 4a-b are redrawn 



in this monograph, PL LXXXVI, figs. 5 and 5a, respectively.) 

 Billingsella whitfieldi (Walcott), Schuchert, 1897, Bull. U. S. Geol. Survey No. 87, p. 159. (Merely changes generic 



reference.) 

 Billingsella whitfieldi Walcott, 1905, Proc. U. S. Nat Mus., vol. 28, p. 246. (Described and discussed as below, an 



almost exact copy of the original description, Walcott 1884b, pp. 18-19.) 



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 fairly convex, elevated along the center to form a flat depressed fold, and 

 sloping somewhat 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 above 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 depression is 

 depressed and corresponds to the flattened lateral slope of the ventral valve. 



Surface marked by fine, very clearly defined concentric striee that are crowded together 

 into narrow ridges, and are subparallel to the front and lateral margins of the shell. 



Billingsella whitfieldi belongs with the group of species including B. salemensis, or shells 

 with coarse plications and very fine concentric striae. The latter species occurs with the Olenel- 

 lus fauna in eastern New York, and B. whitfieldi in the Middle Cambrian of central Nevada. 



The specific name was given in honor of R. -P. Whitfield. 



Formation and locality. — Middle Cambrian: (55b) Top of the Eldorado limestone [see Walcott, 1908f, p. 1841, 

 west side of Secret Canyon; and (55) shaly limestone at the top of the Eldorado limestone [Walcott, 19081, p. 184], east 

 slope of Prospect Mountain, in New York Canyon; both in the Eureka district [Hague, 1892, Atlas], Eureka County, 

 Nevada. 



