188 
Kirtley F. Mather 
by very narrow, rounded, shallow depressions, the plications 
growing progressively smaller and fainter toward the cardinal 
extremities where they become obsolete; mesial sinus shallow, 
originating at the beak as a narrow, simple, well-defined de- 
pression, becoming broader anteriorly, with a flat or gently 
rounded floor occupied by about 3 rounded plications of nearly 
i 
equal size. 
Brachial valve a little less convex than the pedicle, the sur- 
face curving sub-equally from about the middle toward the 
margins; beak projecting only slightly beyond hinge-line, um- 
bonal region not strongly elevated ; plications of lateral slopes 
as in the opposite valve ; mesial fold only slightly elevated above 
the lateral slopes, the depressions which separate it from the 
adjacent plications being much broader but not deeper than i 
those between any two plications elsewhere on the surface, ] 
bearing about 3 sub-equal plications similar to those of the 
lateral slopes. ^ 
Minute surface markings of the shell consist of fine, close- I 
1 
set, wavy, concentric lines of growth which are normally more 
closely crowded and somewhat stronger toward the anterior i 
margin of the larger shells than elsewhere on the surface. Sur- 
face apparently devoid of minute radiate markings. 
Remarks. This species is obviously closely related to B. sub- 
cardiiformis of the Salem limestone, but is distinguished from 
that form by the absence of false area-like regions on either ! 
side of the true cardinal area and by the weaker plications and 
less elevated fold and sinus of the Morrow form. From B, 
sub orbicularis it is distinguished by the proportionately shorter 
hinge-line. 
The species is not very abundant in the Morrow collections, 
being represented by only seven specimens, all from one locality. 
Horizon and locality. Morrow formation : near Choteau, 
Oklahoma (Station 297). 
Genus SQUAMULARIA Gemmellaro 
Squamularia perplexa (McChesney) 
Plate XII, figures 13-1 3b. 
1856, Spirifer lineatus. Hall, Pac. R. R. Rep., vol. 3, p. 101, pi. 2, figs. 
6-8. (Not S. lineatus Martin, 1809). 
Carboniferous: Pecos Village, New Mexico. 
