25 
Pedicle valve very convex at the beak, rounding to the margin evenly 
without any definite fold corresponding to the slight sinus. Teeth, 
triangular, strong, attached to the base of the cardinal area just beyond 
the opening of the delthyrium and strengthened from below by supports 
resting on the cavity of the shell and continuing faintly for a short space 
along the edges of the muscle scar. Scars indistinct, but apparently 
rounded and not projecting beyond the middle of the shell. 
In general outline 0. marshalli somewhat resembles the Anticosti 
specimen 0. laurentina , but the plications of the western species are coarser, 
the pedicle valve more convex, the depression in the brachial valve more 
defined, and none of the specimens preserved has a deltidium covering 
the delthyrium. 
The species is named after Mr. J. R. Marshall, Geological Survey, 
Canada, whose collections from the Kananaskis-Palliser Pass area have 
been productive of much new material from these beds. 
Horizon and Locality. Richmond: Beaverfoot. From several local- 
ities just east of Palliser pass. 
Dinorthis Columbia n. sp. 
Plate V, figures 7, 8, 9, 10 
Shell subquadrate, width greater than length. Hinge-line a little 
more than half the greatest width. Cardinal areas well developed, concave, 
that of the pedicle valve being more incurved and somewhat less elevated 
than is usual in this genus. Striae fifty to sixty in number at the margin 
of a full-grown specimen, rather coarse, angular, with angular troughs 
between, mostly simple on the brachial valve, in some cases a few added 
by implantation near the margin, on the pedicle valve the additions are 
much more numerous and are formed both by implantation and by 
bifurcation. Concentric growth-lines developed on the more mature 
specimens forming a finely ornamented imbricating surface on the last 
third of the shell. In some the imbrication becomes a sharply defined 
line of arrested growth. Umbonal convexity of the pedicle valve in some 
cases almost taking the form of a fold for a short distance from the beak, 
flattening out with the growth of the valve. Brachial valve more convex 
than the pedicle valve, with a broad, shallow sinus beginning at the beak 
and passing over the umbonal region, after which it merges into the general, 
not very pronounced convexity of the valve. 
Area of brachial valve not very high, slightly concave, and with a 
few poorly defined markings radiating from the beak. The interior of 
the brachial valve shows a long septum, rounded on the surface, out of the 
summit of which rise the cardinal process and the crural plates. Cardinal 
process strong, projecting obliquely and filling up the foramen and the 
delthyrium, angular on the external face, having a barbed projection 
on each side, but ending in a point. Seen from below it resembles a spear 
head. The support of the crural plates has its origin in the head of the 
septum which divides at the base of the cardinal process, one arm passing 
on either side and on the edge of the shell forming a callosity, the base 
