PLATE LXXXV. 
a. Cardinal area. d’. Cast of umbonal cavity. 
a’. Anterior adductor impressions. j. Cardinal process. 
b. Dental sockets. o. Ovarian spaces. 
e. Crura. r. Visceral area. 
d. Deltidium. t. Teeth. 
vs. Vascular sinus. 
BILLINGSELLA COLORADOENSIS (Shumard) (p. 751). 
[Text figs. 5, p. 299, and 66, p. 751.] 
Figure 1. Exterior of typical form of ventral valve, from Locality 70, Upper Cambrian limestone on Morgans Creek, 
Burnet County, Texas. U.S. Nat. Mus. Cat. No. 34777b. The surface of this specimen is enlarged 
in figure 1k. It is not the type specimen. 
la. Exterior of a silicified ventral valve, from Locality 302g, Upper Cambrian limestone, north slope of Crow- 
foot Ridge, Yellowstone National Park, Wyoming. U.S. Nat. Mus. Cat. No. 35218a. Copied from 
Walcott [1899, Pl. LX1, fig. 1]. 
lb. Ventral valve, from Locality 5a, Upper Cambrian limestone of the St. Charles formation, 2 miles southeast 
of Malade, Oneida County, Idaho. The radiating strie and concentric ridges of growth are very 
strongly marked on this specimen. Other specimens show the surface characters of figures 1 and le.- 
U.S. Nat. Mus. Cat. No. 51403a. - 
le. Partly exfoliated ventral valve from Locality 68, Upper Cambrian limestone, Packsaddle Mountain, 
Llano County, Texas. U.S. Nat. Mus. Cat. No. 34774a. 
1d. Ventral valve from Locality 97, Upper Cambrian ‘‘St. Croix sandstone,’’ Reads Landing, Wabasha County, 
Minnesota. U.S. Nat. Mus. Cat. No. 34771a. 
le. Dorsal valve associated with the specimen represented by figure 1. U.S. Nat. Mus. Cat. No. 34777c. 
lf. Dorsal valve associated with specimen represented by figure 1. U.S. Nat. Mus. Cat. No. 34777d. 
1g. Dorsal valve associated with specimen represented by figure la. U.S. Nat. Mus. Cat. No. 35213b. Copied 
from Walcott [1899, Pl. LXI, fig. la]. 
lh. Dorsal valve associated with the ventral valve represented by figure 1d. U.S. Nat. Mus. Cat. No. 34771b. 
li. Dorsal valve with strongly marked radiating costs, associated with the specimen represented by figure le. 
U.S. Nat. Mus. Cat. No. 34774b. 
1j. Small dorsal valve showing deep mesial sinus. Locality 131, Upper Cambrian ‘‘St. Croix sandstone,” 4 
miles east of Lake City, Wabasha County, Minnesota. U.S. Nat. Mus. Cat. No. 34770a. 
1k. Enlargement of the surface of the specimen represented by figure 1. 
11. Group of silicified shells associated with the specimen represented by figure la. U.S. Nat. Mus. Cat. 
No. 35218c. 
1m. Interior cast of ventral valve, showing marked vascular sinuses, and a ridge corresponding to a median 
groove. Same locality as specimen represented by figure Id. U.S. Nat. Mus. Cat. No. 34771e. 
In. Impression of interior of ventral valve probably associated with the specimen represented by figure 1d. 
U.S. Nat. Mus. Cat. No. 3477le. Drawn from an artificial cast, the original mold of which can not 
be located. The cast, with another (Cat. No. 34771f) which was used to restore portions of figure In, 
was in a tray with specimens from Locality 97, but it may not belong there. (See fig. lu.) 
lo. Interior of ventral valve associated with the specimen represented by figure la. U.S. Nat. Mus. Cat. No. 
35213d. Copied from Walcott [1899, Pl. LXI, fig. 1c]. 
lp, 1q, and Ir. Casts of interiors of ventral valves from Locality 83°, Upper Cambrian greensand horizon in 
“St. Croix sandstone,’’ Trempealeau, Trempealeau County, Wisconsin. These three figures repre- 
sent unusually convex specimens that may belong to a distinct species. U.S. Nat. Mus. Cat. Nos. 
52235a, 52235b, and 52235c, respectively. 
1s. Cast of the posterior portion of a ventral valve, with side outline. Locality 70a, Upper Cambrian lime- 
stone, Morgans Creek, Burnet County, Texas. U.S. Nat. Mus. Cat. No. 34777e. 
1t. Cast of the interior of a ventral valve, associated with specimen represented by figure la. U.S. Nat. Mus. 
Cat. No. 35213e. Copied with slight alterations from the figure given by Walcott [1899, Pl. LXI, 
fig. 1d]. : 
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