QOI4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Measurements in mm.—Holotype, length 12.1, brachial length 11.0, midwidth 
14.2, hinge width 15.0, thickness 2.9, height 4.7, trail length 6.0. 
Types.—Holotype: 117817a; figured paratype: 117817b; unfigured paratype: 
117817¢. 
Horizon and locality —Arline formation in Virginia: In Porterfield Quarry, 
5 miles east of Saltville, Maccrady (T.V.A. 218-NW) Quadrangle. 
Discussion.—This is one of the earliest members of this genus yet found. The 
species is small, geniculate in the anterior third, and has a diamond-shaped 
muscle area in the pedicle valve. It is similar to O. parvula but differs in having 
pronounced ears, geniculation farther anterior to the beak, and a flatter brachial 
valve. 
OPIKINA MINNESOTENSIS (N. H. Winchell) 
Plate 245, D, figures 21-28 
Strophomena minnesotensis N. H. WINcCHELL, 9th Ann. Rep. Minnesota Geol. Nat. Hist. 
Surv., p. 120, 1881. 
Opikina minnesotensis (N. H. Winchell) Satmon, Journ. Paleont., vol. 16, No. 5, p. 502, 
pl. 87, figs. 5-11, 1942 (complete synonymy). 
Types.—Hypotypes: 24705, 24708a,b, 45277a-c. 
Horizon and locality.—Platteville formation (McGregor member) in Min- 
nesota: At Minneapolis; on U. S. Highway 52, 2 to 3 mles north of Fountain, 
Goodhue County. 
Same formation in Wisconsin: Bluff at Hudson, St. Croix County; Janes- 
ville, Rock County; Mineral Point, Iowa County; Bellville, Dane County; 
Pomeroy’s Quarry, River Falls, Pierce County; quarry at the junction of Wis- 
consin Highways 130 and 23, north of Dodgeville, Iowa County; Rocktown, 
Ripon Center, quarry on Wisconsin Highway 81, 1 mile north of Ellenboro, 
Grant County; Beloit, Rock County. 
Same formation in Illinois: 14 miles northeast of Dixon, Dixon (15’) Quad- 
rangle. 
Discussion.—This species is similar to O. septata internally and externally, 
but the Minnesota species is more convex and has a much larger muscle scar 
in the pedicle valve. 
OPIKINA NASUTA Cooper, new species 
Plate 242, C, figures 11-13a 
Shell of about medium size for the genus, slightly wider than long and with 
the hinge about equal to the midwidth; cardinal extremities nearly a right angle; 
sides gently curved, subparallel; anterior margin narrowly rounded; surface 
costellate; visceral region with obscure concentric wrinkles. 
Pedicle valve with uneven convexity, the posterior two-thirds nearly flat but 
the anterior third abruptly and sharply bent in the direction of the brachial valve. 
Anterior profile strongly domed. Angle of geniculation 115°; umbo narrowly 
swollen to form a short fold; lateral slopes precipitous ; anterior slope long and 
steep; anterior third swollen and narrowed to give a nasute effect to the valve. 
