PLATE LI. 167 
ELxKant ipa (Billings) (p. 563). 
[Pl. XXX, figs. 20 and 20a.] 
Ficures 4 and 4a. Top and side views of a partly exfoliated ventral valve. Geol. Survey Canada. 
4b. Cast of the interior of a dorsal valve, showing elevated visceral cavity and muscle scars. Geol. Survey 
Canada. 
4c. Interior of a ventral valve, preserving a portion of the reversed area. Geol. Survey Canada. 
The specimens represented are all from Locality 319i, limestone No. 2 of Billings’s section, at Point Levis, Quebec. 
Oxo.us (ForDINIA) GILBERTI Walcott (p. 429). 
Ficures 5, 5a, and 5c. Side and top views of ventral valves varying in outline and convexity. U.S. Nat. Mus. Cat. 
Nos. 51946a, 51946c, and 51946d, respectively. Figure 5, the type specimen, is copied from Walcott 
[1908d, Pl. VII, fig. 15]. 
5b. Interiorof dorsal valve. U.S. Nat. Mus. Cat. No.51946b. Copied from Walcott [1908d, Pl. VII, fig. 15a}. 
5d. Exterior of dorsal valve. U.S. Nat. Mus. Cat. No. 51946e. 
The specimens represented are all from Locality 11m, Middle Camprian limestone southeast of Marjum Pass. 
House Range, Utah. ; 
SCHUCHERTINA CAMBRIA Walcott (p. 585). 
Ficures 6, 6’, and 6’. Exterior, side, and back views of a partly exfoliated ventral valve. U.S. Nat. Mus. Cat. 
No. 5141 1a. 
6a. Exterior of a large, partly exfoliated ventral valve with a slight median fold. U.S. Nat. Mus. Cat. No. 
51411b. 
6b. Cast of the interior of a ventral valve, the type specimen, showing flabelliform muscle scars. U.S. Nat. 
Mus. Cat. No. 51411e. 
6c. Interior of the ventral valve represented by figure 6b, drawn from a cast of that specimen. U.S. Nat. 
Mus. Cat. No. 51411c. Parts of this figure are restored from other specimens. 
6d and 6d’. Top, back, and side views of a cast of the interior of a slightly distorted ventral valve. U.S. 
Nat. Mus. Cat. No. 51411d. 
6e. Interior of the ventral valve represented by figure 6d, obtained by making a cast of that specimen. U. S. 
Nat. Mus. Cat. No. 51411d. 
6f. Top and side view of a cast of a dorsal valve. U.S. Nat. Mus. Cat. No. 51411e. 
6g. Exterior of a dorsal valve. U.S. Nat. Mus. Cat. No. 51411f. 
6h. Cast of the interior of a ventral valve. U.S. Nat. Mus. Cat. No. 51411¢. 
6i. Interior of the ventral valve represented by figure 6h obtained by making a cast of that specimen. U. 8. 
Nat. Mus. Cat. No. 51411g. 
6j. Cast of the interior of a dorsal valve, showing mesial area and vascular markings. U.S. Nat. Mus. Cat. 
No. 51411h. 
6k. Enlargement of the central portion of figure 6]. 
61. Cast of the posterior portion of the interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 51411i. 
6m. Interior of the posterior portion of the dorsal valve represented by figure 6 1, obtained by making a cast 
of that specimen. U.S. Nat. Mus. Cat. No. 51411i. 
The specimens represented by figures 6, 6a—m are from Locality 5k, Middle Cambrian limestones on the road to 
Wolsey, about 8 miles south of Neihart, Little Belt Mountains, Montana. 
