PLATE LXXII. 
el. Cardinal sear. vy. Visceral area. 
fa. False area. vs. Main vascular sinus. 
h. Central sear. x’. Cast of foraminal aperture. 
s. Median septum or ridge. x’’. Cast of apical callosity. 
ACROTRETA SAGITTALIS TRANSVERSA (Hartt) (p. 708). 
Fieures 1, 1’, 1’; la, la’, la’; and 1b. Top, side, and back views of casts of interior of three ventral valves. U.S. 
Nat. Mus. Cat. Nos. 52160a, 52160b, and 52160c, respectively. 
le. A ventral valve with a portion of the outer shell. U.S. Nat. Mus. Cat. No. 52160d. 
1d and 1d’. Cast of the interior of dorsal valve, with side view. U.S. Nat. Mus. Cat. No. 52160e. 
le, le’, le’; lf, 1f’, 1i”; and lg, 1g’, le’. Top, back, and side views of casts of interior of dorsal valves. 
U.S. Nat. Mus. Cat. Nos. 52160f, 52160g, and 52160h, respectively. 
th, li, and 1j. Side, dorsal, and back views of a cast of the two valves. U.S. Nat. Mus. Cat. No. 521601. 
1k. Interior of a dorsal valve pressed down on a ventral valve. U.S. Nat. Mus. Cat. No. 52160}. 
The specimens represented are all from Locality 3, Upper Cambrian shaly limestone 300 feet (91.4 m.) above the 
Paradowides zone, Manuels Brook, Conception Bay, Newfoundland. 
ACROTRETA MIsERA (Billings) (p. 695). 
Ficurss 2, 2’, and 2”. Top, side, and back views of cast of ventral valve. U.S. Nat. Mus. Cat. No. 52128m. 
2a, 2a/, 2a/’; 2b, 2b’, 2b’; 2x, 2c’, 2c’; and 2d, 2d’, 2d’. Top, side, and back views of casts of ventral 
valves. U.S. Nat. Mus. Cat. Nos. 52128a-d, respectively. 
2e, 2e’, and 2e”. Top, side, and back views of exterior of ventral valve. U.S. Nat. Mus. Cat. No. 52128e. 
2fand 2¢. Exterior and outline of convexity of two dorsal valves. U.S. Nat. Mus. Cat. Nos. 52128f and 
52128g, respectively. 
2h. Interior of dorsal valve. U.S. Nat. Mus. Cat. No. 52128h. 
2i, 2i/, 21’; 2), 2j’, 2)’; 2k, 2k’, 2k’; and 21,21/,21/’. Top, side, and back views of casts of the interior of 
dorsal valves. U.S. Nat. Mus. Cat. Nos. 52128i-1, respectively. 
The specimens represented are all from Locality 1, Middle Cambrian, shales of zone A of No. 7 of the Manuels 
Brook section [Walcott, 1891b, p. 261], Manuels Brook, Conception Bay, Newfoundland. 
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