FIGURES 
FIGURES 
PLATE LXXI. 
cl. Cardinal scar. y. Visceral area. 
fa. False area. vs. Main vascular sinus. 
h. Central sear. x’. Cast of foraminal aperture. 
s. Median septum. x’’. Cast of apical callosity. 
ACROTRETA SAGITTALIS TACONICA (Walcott) (p. 707). 
1, ’, and 1”. Top, side, and back views of a ventral valve from Locality 37b, Lower Cambrian limestone east 
of Salem, Washington County, New York. U.S. Nat. Mus. Cat. No. 52161a. 
la, la’, and la’. Interior of ventral valve associated with the specimen represented by figure 1. U.S. Nat. 
Mus. Cat. No. 52161b. 
1b, 1b’, 1b’, and le, le’, le’. Top, back, and side views of casts of the interior of ventral valves from Locality 
88a, Lower Cambrian limestone south of North Granville, Washington County, New York. U. 8. 
Nat. Mus. Cat. Nos. 52163a and 52163b, respectively. The type specimen, represented by figure 1c, 
was figured by Walcott [1887, Pl. I, fig. 18b]. 
id, 1d’, and 1d’. Interior of a ventral valve from Locality 44a, Lower Cambrian limestone on Valatie Kill, 
Rensselaer County, New York. U.S. Nat. Mus. Cat. No. 52165a. 
le, le’, and le’’. Interior of a ventral valve associated with the specimen represented by figure 1. U.S. 
Nat. Mus. Cat. No. 52161c. 
lf. Dorsal valve from Locality 36b, Lower Cambrian limestone near Greenwich, Washington County, New 
York. U.S. Nat. Mus. Cat. No. 52166a. 
lg. Exterior and outline of convexity of dorsal valve from Locality 22, Lower Cambrian limestone near North 
Granville, Washington County, New York. U.S. Nat. Mus. Cat. No. 52164a. 
lh. Exterior and outline of convexity of dorsal valve from Locality 86, Lower Cambrian limestone south of 
Shushan, Washington County, New York. U.S. Nat. Mus. Cat. No. 17441a. Specimen figured by 
Walcott [1887, Pl. I, fig. 18e]. 
li and 1j. Casts of the interior and outline of convexity of dorsal valves associated with the specimen repre- 
sented by figure 1. U.S. Nat. Mus. Cat. Nos. 52161d and 52161e, respectively. 
1k. Interior of a dorsal valve associated with the specimen represented by figure 1. U.S. Nat. Mus. Cat. 
No. 521611. 
1], 11’, and 1m, 1m’. Casts of the interior, with back view and outline of convexity, of two dorsal valves 
associated with the specimen represented by figure 1. U.S. Nat. Mus. Cat. Nos. 52161¢ and 52161h, 
respectively. 
In. Cast of the interior and outline of convexity of dorsal valve associated with the specimen represented 
by figure 1. U.S. Nat. Mus. Cat. No. 521611. 
lo. Interior of a ventral valve from Locality 34, Lower Cambrian limestone at Low Hampton, Washington 
County, New York, showing the apical callosity and fine grooves radiating forward from it. U.S. 
Nat. Mus. Cat. No. 52162b. Another specimen (Cat. No. 52163c, Locality 88a) was used to restore 
certain portions of this figure. Specimen figured by Walcott [1887, Pl. I, fig. 18a]. 
AOROTRETA SAGITTALIS (Salter) (p. 704). 
2, 27, 2/7; 2a, 2a’, 2a’’; 2b, 2b’, 2b’; and 2c, 2c’, 2c’’. Top, side, and back views of casts of the interior of four 
ventral valves from Locality 8w, Middle Cambrian limestones at Andrarum, Province of Christianstad, 
Sweden. U.S. Nat. Mus. Cat. Nos. 52156a, 52156b, 52156c, and 52156d, respectively. 
2d, 2d’, and 2f, 2i”. Top and back views of two dorsal valves from Locality 6i, Middle Cambrian limestone 
near Fosters Point, Random Sound, Newfoundland. U.S. Nat. Mus. Cat. Nos. 52152a and 52152b, 
respectively. 
2e and 2e’. Top and back views of dorsal valve from Locality 2s, Middle Cambrian limestones at Hastings Cove, 
Kennebecasis Bay, St. John County, New Brunswick. Museum?. 
2¢. Back view of ventral valve. From Borregaard, Bornholm, Denmark (horizon unknown). Copenhagen 
University Museum. 
2h. Back view of cast of dorsal valve. From Borregaard, Bornholm, Denmark (horizon unknown). Copen- 
hagen University Museum. . 
3, 3’, 3, and 3a, 3a’, 3a’. Top, back, and side views of casts of the interior of ventral valves from Locality 
318g, Middle Cambrian shales near St. Davids, South Wales. U.S. Nat. Mus. Cat. Nos. 52155a and 
52155b, respectively. 
3b, 3c, 8d, and 3e. Ventral, side, back, and dorsal views of a cast of the two valves united from Locality 8w, 
Middle Cambrian limestones at Andrarum, Sweden. U.S. Nat. Mus. Cat. No. 52156e. 
3f. Cast of a ventral valve with truncated apex, associated with the specimen represented by figure 3. U.S. 
Nat. Mus. Cat. No. 52155c. e 
3g, 3g’, 3g’, and 3h, 3i, and 3j. Casts of the interior of four dorsal valves, with outlines of convexity. Asso- 
ciated with the specimen represented by figure 3. U.S. Nat. Mus. Cat. Nos. 52155d, 52155e, 52155f, 
and 52155g, respectively. 
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