23 
Rhynchotrema kananaskia n. sp. 
Plate IV, figures 14, 15, 16, 17, 18 
Shell of moderate size, breadth a little greater than length, average 
breadth 15 to 17 mm., convexity not so pronounced as in many species 
of this genus. In old age, however, the gibbosity of the shell greatly 
increases. Beak of the brachial valve incurving, enclosed by that of the 
pedicle valve which projects somewhat beyond it. Fold and sinus well 
marked, but not so deep as in R. capax or R. windermeris. Striae simple, 
rather angular, four on the fold and three in the sinus in most cases, but 
three on the fold and two in the sinus are not infrequent with seven to nine 
on the sides. Zigzag growth lines produce an ornamentation similar to 
R. capax. 
Brachial valve convex, but in many specimens after the greatest 
convexity is reached there is a flattened outline, passing from the convexity 
of the umbonal region to the anterior margin, best seen in a profile view. 
Pedicle valve less convex and more narrowly triangular than the brachial. 
Several unsuccessful attempts were made to “eat out” the interior 
filling, but it appears to be insoluble in acid. 
R. kananaskia is easily distinguished from the previously described 
species of Rocky Mountain Rhynchotremas. In its ornamentation and 
general form it is allied to R. capax , but it is smaller and although having 
the tendency towards a gibbous form in its gerontic stages, the average 
mature specimen is not so convex, the beak, particularly that of the pedicle 
valve, is more projecting, the striae are finer and more numerous on the sides. 
The species is larger than R.7 anticostiensis and wider in proportion 
to its length, making a less triangular outline. The beak is less acuminate. 
At 95 feet above the base of the Beaverfoot in the section at the head 
of Windermere creek, one specimen was found having an extra plication 
on the edge of the slope limiting the sinus, making five plications, three 
in the floor of the sinus and two on the slopes; the opposite valve is not 
sufficiently preserved to show whether there is a corresponding extra pair 
on the fold. The specimen is very gibbous and it has every appearance 
of being a condition of a gerontic stage of development. 
Horizon and Locality. Richmond: Beaverfoot. From several local- 
ities east of Palliser pass, from the cherty beds northeast of mount 
McMurdo, Beaverfoot range, and from 95 feet above the base of the Beaver- 
foot at the head of Windermere creek, British Columbia. 
Plectorthis ? sinuatis n. sp. 
Plate IV, figures 19, 20, 21 
Shell small, rather flat, breadth twice the length, average length 
10 mm., width 5 mm. Greatest width at hinge-line. Cardinal angles 
sharp. Sides narrowing down somewhat towards the anterior margin, 
which is subparallel to the hinge-line, producing a form almost oblong 
in outline. Striae very fine, increasing by bifurcation, many of the same 
striae dividing twice, primary and secondary in many cases so grouped 
as to result in a fascicular ornamentation, crossed by very fine concentric 
growth lines, more evident near the anterior margin. 
