PLATE LXVI. 
a’. Outer lateral space of area. s. Median septum or ridge. 
el. Cardinal scar. vs. Main vascular sinus. 
fp. False pedicle groove. x’’. Cast of apical callosity. 
h. Central muscle scar. 
ACROTRETA GEMMA Billings (p. 685). 
Fieures 1, 1’, 1”, and la, la’, la’’. Top, side, and back views of two ventral valves from Locality 314d, Lower Ordovi- 
cian limestone 4 miles northeast of Portland Creek, Newfoundland. Mus. Geol. Survey Canada. 
Figure 1 may be taken as the type. 
1b. Enlargement of the apex and foraminal opening of a ventral valve associated with the specimens repre- 
sented by figures 1 and la. 
Figures 1, la-b are drawn from the specimens illustrated by Billings [1865, figs. 201b, d, e, and f]. 
AcCROTRETA OVALIS Walcott (p. 699). 
Ficures 2, 2a, and 2b. Top, side, and back views of the type specimen, a ventral valve, from Locality 314d, Lower 
Ordovician limestone 4 miles northeast of Portland Creek, Newfoundland. Mus. Geol. Survey Canada. 
ACROTRETA GEMMULA Matthew (p. 686). 
[Pl]. LX XVII, figs. 5, 5a-f.] 
Ficures 3, 3’, and 3’. Top, back, and side views of the outer surface of a ventral valve (locality unknown). Univer- 
sity of Toronto, Canada. 
3a. Top, back, and side views of the cast of the interior of a ventral valve in which the cast of the base of the 
foraminal tube is unusually large. Locality 301a, Middle Cambrian sandstones in Division 1b3 of 
Matthew on Haniord Brook, St. John County, New Brunswick. University of Toronto, Canada. 
Type specimen, figured by Matthew [1894, Pl. XVI, fig. 2a]. 
3b and 3c. Cast and interior of a dorsal valve from the locality represented by figure 3a. University of 
Toronto, Canada. Specimen figured by Matthew [1894, Pl. XVI, fig. 2b]. 
ACROTRETA’ SAGITTALIS MAGNA (Matthew) (p. 706). 
Ficures 4 and 4a. Top and side views of a cast of the interior of a ventral valve from Locality 2s, Middle Cambrian 
limestone at Hastings Cove, northeast of St. John, New Brunswick. University of Toronto, Canada. 
Specimen figured by Matthew [1897b, Pl. I, fig. 1b] as Linnarssonia belti magna. 
4b. Cast of the interior of a dorsal valve from the locality represented by figure 4. University of Toronto, 
Canada. Type specimen, figured by Matthew [1897b, Pl. I, fig. la] as Linnarssonia belti magna. 
4e, 4c’, and 4c’. Top, back, and side views of a small well-preserved ventral valve from Locality 21, Middle 
Cambrian limestone on Hanford Brook, St. John County, New Brunswick. U. 8. Nat. Mus. Cat. 
No. 35284a. & 
4d. Interior of a partly crushed ventral valve associated with the shell represented by figure 4c. U.S. 
Nat. Mus. Cat. No. 35284b. 
4e and 4f. Interior of a dorsal valve and natural cast of same associated with the shell represented by figure 4c. 
U.S. Nat. Mus. Cat. Nos. 35284c and 35284d, respectively. 
ACROTRETA GRACIA Walcott (p. 687). 
Fieures 5, 5’, and 5’. Top, back, and side views of a ventral valve. U.S. Nat. Mus. Cat. No. 35272a. 
: a, 5a’, and 5a/”. Top, back, and side views of a cast of a ventral valve, the type specimen. U.S. Nat. Mus. 
Cat. No. 35272b. , 
5b. Cast of part of the interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 35272c. 
5c and 5c’. Top, side, and back views of a cast of a dorsal valve. U.S. Nat. Mus. Cat. No. 35272d. 
5d. Cast of the exterior of a dorsal valve, with a portion of the posterior part of the shell. U.S. Nat. Mus. 
Cat. No. 35272e. 
5 
5 
The specimens represented are all from Locality 2s, Middle Cambrian limestone at Hastings Cove, on Kennebecasis 
Bay, northeast of St. John, New Brunswick. 
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