246 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
ACROTRETA GEMMA Billings 
Plate 22, E, figures 10, 11 
Acrotreta gemma Biturncs, Geol. Surv. Canada, Paleozoic fossils, vol. 1, p. 216, figs. 201a-f, 
1865.—Watcott, U. S. Geol. Surv. Mon. 51, p. 685, pl. 66, figs. 1a, b, 1912. 
One specimen of two present in the National Collection is worthy of remark. 
Both are pedicle valves, and one of them seems to be a perfectly normal indi- 
vidual with a pseudointerarea and intertrough as described by Billings and 
Walcott. The second specimen has a perfectly formed pseudointerarea, but the 
median part of that surface is elevated to form a gradually widening ridge from 
beak to base. The structure suggests the homoeodeltidium of the Paterinacea. 
The structure is too regular to be a deformity, but more specimens are needed 
to understand it. 
Figured specimen.—116816a. 
Horizon and locality Upper Table Head series in Newfoundland: At Table 
Point Cove. 
ACROTRETA MAGNA Cooper, new species 
Plate 28, D, figures 9-12 
Shell large for the genus, forming a depressed cone in profile; outline subellip- 
tical; surface marked by fine concentric elevated lines. 
Pedicle valve forming a posteriorly truncated cone in lateral profile; anterior 
slope long and moderately convex ; beak posterior to the center; posterior slope 
shorter than the anterior one, very steep and gently convex. Anterior profile 
broadly convex and with convex sides. Apical angle 75°? Pseudointerarea 
broad ; intertrough narrow and deep. 
Brachial valve elliptical in outline with the width slightly greater than the 
length; hinge wide and straight; posterolateral extremities narrowly rounded ; 
sides gently rounded and anterior broadly rounded. Lateral profile gently con- 
vex, with the maximum convexity in the umbonal region; anterior portion flat- 
tened ; anterior profile broadly convex with the maximum convexity at the mid- 
dle; lateral slopes long and gently concave. Median septum extending from the 
posterior margin to about the middle of the valve; 2 large muscle scars located 
on each side of the median ridge just anterior to the hinge are visible. 
Measurements in mm.— 
Length Width Thickness 
Holotype (pedicle valve) ........cceesceccees 5.5 6.8 2.7-+- 
Paratype (brachial valve 109724b) ..........- 8.3 6.4 ? 
Types.—Holotype : 109724a; figured paratype: 109724b; unfigured paratypes: 
109724c-f, 
Horizon and locality.—Boulders of the Mystic conglomerate in Quebec, Can- 
ada; Range 6, Lot 20, 24 miles north of Mystic, Stanbridge Township. 
Discussion.—This species has been assigned to Acrotreta rather than to Cono- 
treta because of its earlier age than Conotreta and because only the bases of 2 
pallial trunks could be distinguished. The extreme inner ends of the pallial trunks 
only are visible, and no evidence of branching could be seen. Actually it cannot 
be determined whether or not the trunks do branch. 
