PLATE LXXXVI. 
a. Cardinal area. d’’. Umbonal cavity. 
b. Dental sockets. j. Cardinal process. 
ec. Crura. o. Ovarian areas. 
d’. Cast of umbonal cavity. vs. Vascular sinus. 
BILLINGSELLA Magor Walcott (p. 758). 
Figure 1. Portion of ventral valve, showing cast of cardinal area and surface cost. Locality 116, Upper Cambrian 
sandstone on Wells farm, 2 miles (3.2 km.) west of Baraboo, Sauk County, Wisconsin. U.S. Nat. 
Mus. Cat. No. 52256a. 
la. Cast of compressed dorsal valve, the type specimen, associated with the specimen represented by figure 1. 
U.S. Nat. Mus. Cat. No. 52256b. 
Figures 1 and la are copied from Walcott [1908d, Pl. X, figs. 1 and la]. 
BILLINGSELLA ORTENTALIS (Whitfield) (p. 759). 
Figure 2. Type specimen, compressed in shale. Locality 319g, Lower Cambrian shales in Parker’s quarry, near 
Georgia, Franklin County, Vermont. Copied from Whitfield [1884, Pl. XIV, fig. 6] where it is 
figured as Orthisina orientalis. 
2a and 2b. Ventral and dorsal valves, from Locality 25a, Lower Cambrian limestone 2 miles (3.2 km.) east of 
Swanton, Franklin County, Vermont. U.S. Nat. Mus. Cat. Nos. 52262a and 52262b, respectively. 
BILLINGSELLA PLICATELLA Walcott (p. 759). 
[Text fig. 1, p. 299.] 
Ficure 3. Exterior and side views of a ventral valve with rather strongly marked fasciculate coste. U.S. Nat. 
Mus. Cat. No. 52263a. 
3a. Exterior and side views of ventral valve with strong coste. U.S. Nat. Mus. Cat. No. 52263b. 
3b. Exterior view of ventral valve on which the surface has been partly smoothed by attrition. U.S. 
Nat. Mus. Cat. No. 52263c. 
3c. Exterior and side views of a very convex ventral valve, marked by very fine radiating strie and faint 
coste. U.S. Nat. Mus. Cat. No. 52263d. 
3d. Exterior of a small, strongly costate ventral valve from Locality 151, Upper Cambrian limestone in point 
overlooking Churn Canyon, west side of the Bridger Range, Gallatin County, Montana. U.S. Nat. 
Mus. Cat. No. 52265a. 
3e. Exterior of a small, strongly costate dorsal valve. U.S. Nat. Mus. Cat. No. 52263e. 
3f. Exterior of ventral valve, partly smoothed by attrition. U.S. Nat. Mus. Cat. No. 52263f. 
3g. Partly exfoliated ventral valve. U.S. Nat. Mus. Cat. No. 52263g. 
3h. Exterior and side view of dorsal valve smoothed by attrition. U.S. Nat. Mus. Cat. No. 52263h. 
3i. Cast of interior of ventral valve, the type specimen, showing cardinal area, a; cast of vascular sinus, vs; 
and ovarian areas, 0. U.S. Nat. Mus. Cat. No. 522631. 
3j. Cast of interior and side outline of a transverse ventral valve. U.S. Nat. Mus. Cat. No. 52263]. 
3k. Cast of interior and side outline of ventral valve, on which the vascular and other impressions are strongly 
marked. U.S. Nat. Mus. Cat. No. 52263k. 
31. Cast of the interior of dorsal valve. U.S. Nat. Mus. Cat. No. 52263 1. 
3m and 3n. Interiors of small, strongly marked ventral and dorsal valves from Locality 4j, Middle Cambrian 
limestones at the head of Deep Creek, Canyon quadrangle (U.S. Geol. Survey), Yellowstone National 
Park, Wyoming. U.S. Nat. Mus. Cat. Nos. 52266a and 52266b, respectively. 
With the exception of figures 3d, 3m, and 3n, all of the specimens represented are from Locality 158, Upper 
Cambrian limestone north of East Gallatin River, near Hillsdale, Threeforks quadrangle (U. S. Geol. Survey), 
Gallatin County, Montana. 
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