gi2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
OPIKINA INQUASSA (Sardeson) 
Plate 245, B, figures 9-12 
Strophomena inquassa SARDESON, Minnesota Acad. Nat. Sci., Bull. 3, p. 334, pl. 5, figs. 22-24, 
1802. 
Opikina inquassa (Sardeson) SAtmon, Journ. Paleont., vol. 16, No. 5, p. 593, pl. 87, 
figs. 12-14, 1942 (for complete synonymy). 
Type.—Hypotype: 24206. 
Horizon and locality—Decorah formation (Guttenburg member, Stictopora 
bed) in Minnesota: At Minneapolis. 
OPIKINA LIRATA Cooper, new species 
Plate 247, F, figures 17-25 
Shell large for the genus, subrectangular in outline, wider than long and with 
a variable hinge; sides moderately rounded; anterior margin broadly rounded; 
costellae differentiated as usual in the genus, 2 to 4 at the front in I mm., I to 3 
of these usually of the finer grade. Valves often plaited by interruptions in growth 
stages. 
Pedicle valve fairly strongly convex in lateral profile and with the maximum 
convexity located at the middle or slightly anterior to the middle; anterior pro- 
file moderately to strongly and broadly domed. Not strongly geniculate, the 
bending usually fairly broad and rounded; posterior gently convex; anterior 
slope convex, long and steep; lateral slopes less steep than the anterior one. 
Umbonal region somewhat swollen. Pseudodeltidium small, depressed inward. 
Interarea short. Muscle field large, occupying about half the inner surface. 
Brachial valve deeply concave in the median region; posterior region gently 
concave; side moderately folded toward the brachial valve; anterior margin 
strongly deflected toward the brachial valve. Interior with subdued septa, stout 
cardinal process. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness Height 
Holotype! +. i223 ean 23.2 21.7 30.0 24.5 3.6 7.0 
Paratype (117816a)..... 24.2 22.8 32.0 29.0+ 3.8 7.8 
4 (CTF7BT6b) 2 pies 23.7 22.6 28.3 24.4 2.7 7.0 
Types.—Holotype: 117816d; figured paratypes: 117816a-c,f; unfigured para- 
types: 117816e,g. 
Horizon and locality—Decorah formation (Ion member) in Minnesota: From 
a road cut 1.1 miles east of U. S. Highway 52 on the south edge of Cannon 
Falls ; Fountain and Kenyon, Goodhue County. Twin City Brick Quarry, south- 
east St. Paul. 
Discussion—This is a fairly large and strongly convex shell broadly and 
deeply open when viewed from the side of the brachial valve. It is suggestive 
of O. expatiata, and comparison between the two is made under that species. 
Compared with other Minnesota species it is larger than O. inquassa and is less 
pronouncedly geniculate than that species. 
