PLATE LXVI. 223 
ACROTRETA CONVEXA Walcott (p. 682). 
Ficure 6. Cast of the interior of a ventral valve, the type specimen, from Locality 3n, Upper Cambrian sandstones 
on Salmon River, Gillis Hill, Cape Breton, Nova Scotia. U.S. Nat. Mus. Cat. No. 35268a. 
6a. Cast of the interior of a dorsal valve associated with the shell represented by figure6. U.S. Nat. Mus. Cat. 
No. 35268b. 
6b, 6b’, and 6b’. Top, side, and back views of the cast of a ventral valve from Locality 10i, Upper Cambrian 
shale on Barachois River, just north of the Boisdale Road, Cape Breton, Nova Scotia. U.S. Nat. 
Mus. Cat. No. 52084a. 
6c. Cast of interior of dorsal valve from Locality 10e, Upper Cambrian shales on east branch of Barachois 
River, north of the crossread from Boisdale to Upper Leitches Creek, Cape Breton, Nova Scotia. 
U.S. Nat. Mus. Cat. No. 52085a. 
ACROTRETA BISECTA Matthew (p. 678). 
Ficures 7, 7’, and 7’’. Top, side, and back views of a par‘ly exfoliated ventral valve. U.S. Nat. Mus. Cat. No. 
52073a. 
7a, 7a’, and 7a/’. Top, side, and back views of cast of ventral valve. U.S. Nat. Mus. Cat. No. 52073b. 
7b. Interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52073c. 
7b’. Enlargement of the area of figure 7b. 
7c. Cast of the interior of a dorsal valve on which the lines of growth about the cardinal scars are beau- 
tifully shown. U.S. Nat. Mus. Cat. No. 52073d. 
7d. Cast of the interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52073e. 
The specimens represented by figures 7, 7a-d are from Locality 3q, Upper Cambrian shale in Barachois Glen, 
south of Little Bras d’Or Lake, Cape Breton, Nova Scotia. 
Ficure 7e. Cast of the interior of the posterior portion of a ventral valve in which the cast of the main vascular sinuses 
is finely preserved; also the cast of the base of the pedicle tube. Locality 10e, Upper Cambrian shales 
on east branch of Barachois Raver, north of crossroad from Boisdale to Upper Leitches Creek, Cape 
Breton, Nova Scotia. U.S. Nat. Mus. Cat. No. 52077a. 
ACROTRETA DEPRESSA (Walcott) (p. 683). 
Ficaures 8 and 8’. Top, side outline, and back view of the type specimen, a cast of the interior of a compressed ventral 
: valve, from Locality 14s, Middle Cambrian shaly limestones (Ogygopsis zone) on Mount Stephen, 
British Columbia. U.S. Nat. Mus. Cat. No. 52086ce. Copied from Walcott [1908c, Pl. I, fig. 3c]. 
8a and 8b. Casts of the interior of two dorsal valves associated with the shell represented by figure 8. U.S. 
Nat. Mus. Cat. Nos. 52086a and 52086b, respectively. Figure 8a is copied from Walcott [1908c, Pl. I, 
fig. 3b]. 
8c, 8c’, and 8c’”’. Top, side, and back views of a ventral valve occurring in the same beds with the specimens 
represented by figures 8, 8a—b, but which is very doubtfully referred to this species. U.S. Nat. 
Mus. Cat. No. 52086d. Figures 8c and 8c’ are copied from Walcott [1908c, Pl. I, figs. 3 and 3a, 
respectively]. 2 
