“y 
358 PALEOZOIC PALEONTOLOGY. 
others anteriorly in a narrow mesial fold. The surface is also marked 
by concentric lines of growth, which usually become more crowded 
toward the margin. 
The dimensions of a rather small specimen are: length, 13 mm.; 
width, 15 mm.; thickness, 4 mm. 
ANOPLOTHECA DICHOTOMA (Hall). 
Plate XLIX., Figs. 3-6. 
1859. Leptocelia dichotoma Hall, Pal. N. Y., vol. IIL, p. 452, pl. 
103 B, figs. 3 a-e. 
Description.—Shell broadly subovate in outline, concavo-convex. 
Pedicle valve strongly convex, its greatest elevation near the middle, 
with a flat-topped mesial elevation, from which the surface slopes 
away to the lateral margins; beak sharply pointed, incurved. Brachial 
valve flattened laterally, with a rather broad, ill-defined mesial sinus 
extending from the beak to the front margin. Surface of each valve 
marked by from fourteen to sixteen rounded or subangular, radiating 
plications, which increase by bifurcation, although in some cases the 
bifurcations are so close to the beak that the plications almost seem 
to be simple. The plications are crossed by a few sublamellose, con- 
centric lines of growth. 
The dimensions of a nearly-perfect specimen are: length, 9 mm.; 
width, 10 mm.; thickness, 4 mm. 
Remarks.—This shell resembles A. concava of the Helderbergian 
fauna, but is a much larger species. Schuchert* has suggested that 
it is possibly the young of L. flabellites, but specimens having the 
characteristics of the species seem to be adult shells. 
* Bull. U. S. G. S., No. 87, p. 144. 
