652 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Discussion —This species suggests a small R. laticosta (Winchell and Schu- 
chert) but is more numerously costate. The species resembles R. rotunda but 
does not attain the large size of that species nor does it have as deep a sulcus. 
This species as here identified is somewhat variable. More extensive collections 
will probably indicate further refinement of the species. 
ROSTRICELLULA TRIANGULATA Cooper, new species 
Plate 133, A, figures 1-11 
Camarotoechia pristina TWENHOFEL and WuiITING (not Raymond), Geol. Soc. Amer. Special 
Pap. 15, p,. 52, pl. 8, figs, 1:2; 1978. 
Shell small, triangular in outline with acute beak (72°) and nearly straight 
sides to the anterolateral extremities which are narrowly rounded. Anterior 
margin broadly rounded. Brachial valve slightly deeper than the pedicle valve. 
Surface costate, sulcus occupied by 4 or 5 costae, the fold by 5 or 6, and the 
flanks by about 5. 
Pedicle valve gently but evenly convex in lateral profile, posterior half mod- 
erately convex, with a long narrow beak and narrowly rounded umbo; sulcus 
originating about 4 mm. anterior to the beak and near the middle of the valve, 
shallow, flat to convex in profile; tongue short and broadly rounded. An- 
terolateral extremities moderately elevated; flanks narrowly convex and with 
steep lateral slopes. 
Brachial valve gently convex with the maximum convexity in the median 
region; broadly convex in anterior profile; fold not conspicuous, only slightly 
elevated at the front; flanks rounded and with moderately steep slopes. 
Measurements in mm.— 
Brachial 
Length length Width Thickness 
Polotypet.t wrens daha sels Mode eee ve 6.4 7.2 4.0 
PAGANO: ao ace th Scos shot ase bdors ane 6.7 6.1 6.0 33 
Types.—Holotype: 111549a; figured paratype: 111549b. 
Horizon and locality—Mingan formation (60 to 70 feet above the base) : 
Bald Island, Mingan group, St. Lawrence River, Quebec, Canada. 
Discussion.—This species differs from R. pristina, with which it was formerly 
confused, in its more triangular form and more numerous costae in the fold and 
sulcus. It differs in the same respects from R. basalaris. It is more finely costate 
than Fe. costata and is not so deep as that species. 
ROSTRICELLULA TRUNCATA Cooper, new species 
Plate 134, B, figures 19-26 
Shell of about medium size for the genus, wider than long, and broadly tri- 
angular in outline. Apical angle about 100°. Posterolateral margins straight, 
anterolateral extremities narrowly rounded; anterior margin truncated. Costae 
strong, narrowly rounded, 4 on the fold, 3 in the sulcus, and 4 to 6 on the flanks. 
Pedicle valve shallow and only gently convex in lateral profile, broadly concave 
