22 
cardinal process is minute, and the whole cleft and hinge-plate is placed 
at an angle so that the end of the septum appears to support it from below 
at right angles, rather than continuing in the same line as the linear cardinal 
process and crural cavity, as in R. i ncrebescens. 
Horizon and Locality. Richmond: Beaverfoot. Three-fourths mile 
east of Palliser pass and from the Stoddart Creek section, Windermere 
district, British Columbia. 
Rhynchotrema pisina n. sp. 
Plate IV, figures 11, 12, 13 
A small, round, pea-like species of Rhynchotrema , a little greater in 
breadth than in length, some attaining the size of a small R. increbescens 
var. occidens, but rounder; the average specimen is considerably smaller. 
Beaks incurved, fold inconspicuous, hardly more than the enlarging of the 
four central strise, sinus more distinct than fold. Striae angular, fourteen 
to sixteen in number, the enlargement of the four central ones practically 
constituting the fold, the five or six on each side being much finer. The 
whole crossed by growth lines producing the Rhynchotrema capax ornament- 
ation on a finer scale. 
Brachial valve very convex, showing a slight median depression at 
the beak that disappears after passing over the umbonal region and usually 
marks the septum in the interior. The inconspicuous fold alters the 
anterior margin but veiy slightly. Only one brachial interior was produced, 
showing the crural plates in the same plane as the hinge-plates and 
tapering into two thread-like elongations produced in the same plane, 
not turned towards the other valve as is the case in R. increbescens and in 
a less degree in R . increbescens var. occidens. The cardinal process is not 
preserved, but it must have, been very minute. Septum thin, plate-like, 
with the narrow edge towards the cavity of the shell, supporting the 
amalgamated hinge-plates at right angles from behind. 
Pedicle valve less convex than the brachial, sinus more distinct than 
the fold of the brachial valve, altogether giving it a more triangular outline 
than that of the other valve. Beak overlapping the brachial beak, and 
less incurved. Interior not known. 
R. pisina is readily distinguished from other species by its small round 
form when both valves are present, by the minuteness of the cardinal 
process, and the elongations of the crural plates on the plane of the hinge- 
plate. The detached pedicle valve tends to grade up to the size and shape 
of R. increbescens occidens and is easily confused with small specimens 
of that species. 
Horizon and Locality , Richmond: Beaverfoot. From the chert beds 
of the Beaverfoot range, from the Fairmont Springs and the Stoddart 
Creek sections, Windermere district, British Columbia. 
