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with flat-bottomed troughs between, troughs a little wider than striae, 
the latter increasing on both valves mainly by implantation, the numerous 
additional striae rapidly attaining the size of the original ones. There 
are two outstanding periods when the striae are increased, one when the 
shell has attained a third of its growth, the other a few millimetres from 
the margin. Concentric growth lines very prominent on the more convex 
brachial valve, less so on the few pedicle valves obtained. 
Cardinal area of the brachial valve very narrow and inconspicuous, 
almost concealed by the beak. The interior shows a rather prominent 
septum, out of whose summit rises a stout bifid cardinal process. At the 
base of the cardinal process the septum divides, each branch curving 
around and forming a support to the crural plates. The crural plates 
are flat, the narrower edge presented to the opposite valve, and on the 
plane of the narrow cardinal area to which they are attached for the first 
third of their length, the dental sockets being formed between the thick- 
ened wall of the shell and the projecting part of the crural plates. 
Area of pedicle valve much more prominent than that of the brachial 
valve, rather high, slightly concave, especially near the beak. Delthyrium 
a broad triangle. Teeth strong, partly destroyed in the interior of the 
valve preserved. The dental lamellae are well developed, and the callosity 
is prolonged around the obcordate muscle area. The three types of 
muscles are well marked. The long, somewhat narrow inductor muscle 
scars are expanded and rounded anteriorly. Flanking them behind are 
the shorter adjustor scars, and on an elevated ridge between them the 
almost linear scars of the adductor muscles. 
Externally D. rockymontana is readily distinguished from other 
species by its fine strise and conspicuous concentric growth lines. Inter- 
nally it is differentiated from other species by the lobed cardinal process 
in the brachial valve and the form of the muscle scars in the pedicle valve, 
especially the raised base of the elongate adductor scars. 
Horizon and Locality. Richmond: Beaverfoot. From Palliser Pass 
district, Rocky mountains, B.C. 
Family, Strophomenidae 
Subfamily, rafine so tjtnnae 
Petroria gen. nov. 
(Petros = rock, ’opos = mountain) 
Small brachiopods, semicircular in outline, pedicle valve convex, 
brachial valve concave, narrow but definite cardinal area on both valves. 
Surface in the early stages of growth covered with fine striae, crossed by 
fine growth lines, becoming greatly accentuated towards maturity, giving 
the shell a very striking appearance. Pedicle valve having a small, round 
perforation, delthyrium covered by a convex deltidium. Teeth rather 
small. Brachial valve with a cardinal process consisting of two stout 
apophyses which quite fill the foramen and project beyond the plane 
