650 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
convex; apical angle about 115°; sulcus occupied by 4 to 6 costae, fold by 5 to 
7 costae, flanks with 9 costae. Surface marked by fine fila, often papillose. 
Pedicle valve gently convex in lateral profile ; broadly convex in anterior pro- 
file but with the median region gently concave. Sulcus originating about 6 mm. 
anterior to the beak ; umbo somewhat swollen. Sulcus broad and shallow; tongue 
moderately long. Median area swollen. Flanks flattened, moderately steep. 
Brachial valve deeper than the pedicle valve, strongly convex in lateral profile, 
broadly arched in anterior profile. Umbo swollen; median region swollen and 
forming the most convex part of the valve; umbo moderately sulcate; fold low 
and with rounded profile; width of fold at front about one-third the valve width. 
Flanks rounded but with moderate slopes. 
Measurements in mm.— rr ahil 
Length length Width Thickness 
Holotype es eS Ae Ga. 117 9.9 13.7; 8.6 
Paratype |\(30550b) vss i. Circe 11.0 9.9 13.4 9.1 
¥ GsGshoe) messed l.ceb 426 0.1 8.6 LL7 6.6 
1 C:2D550d))« Bix sis ators afeh 8.2 Ue 8.8 5.3 
Types—Holotype: 36550a; figured paratype: 36550b; measured paratypes: 
365 50c,d. 
Horizon and locality —Swift Current formation in Ontario, Canada: North- 
east corner of St. Joseph Island, St. Marys River. 
Discussion.—This species has been referred to R. ainslei and is quite suggestive 
of that form because of its rounded contours, low beak, and transversely ellip- 
tical outline. In spite of the similar appearance it is quite different. Rostricel- 
lula rotunda is generally smaller than R. ainslei, is more rotund in lateral profile, 
and has a lower and narrower fold. 
ROSTRICELLULA SUBTRANSVERSA Cooper, new species 
Plate 137, B, figures 7-19 
Shell of about medium size for the genus, wider than long, with narrowly 
rounded sides and somewhat truncated anterior margin. Apical angle varying 
between go° and 100°. Sulcus marked by 5 or 6 costae, the fold by 6 or 7, and 
the flanks by 6 to 10 costae. Entire surface crossed by fine elevated fila. 
Pedicle valve gently convex in both profiles; umbo convex, beak strongly in- 
curved. Sulcus originating 4 to 5 mm. anterior to the beak, broad and shallow. 
Tongue moderately long. Flanks narrowly rounded and with moderate slopes. 
Brachial valve considerably deeper than the pedicle valve, strongly convex in 
lateral profile, and strongly arched with steep sides in anterior profile. Fold low, 
not strongly defined at any point on its length; median region strongly inflated ; 
flanks swollen and precipitous. 
Measurements in mm.— cables 
Length length Width Thickness 
Holbetype’t soriwicetaun oidvins: oak 9.8 8.8 12.1 7.6 
Paratype Cri 72280) ids OSL. 12.3 11.5 13.0 9.7 
(1172286). esteeqer peas a2 >} 8.6 II.0 5.4 
