942 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
STROPHOMENA MOLLIS Wilson 
Strophomena mollis Witson, Trans. Roy. Soc. Canada, ser. 3, vol. 39, sec. 4, p. 136, pl. 1, 
fig. 4, 1945; Geol. Surv. Canada, Bull. 8, p. 105, pl. 9, fig. 4, 1046. 
Type.—Holotype: G.S.C. 7588. 
Horizon and locality —lLeray =Chaumont formation in Ontario, Canada: At 
Lots 3-5, concession III R. F., Gloucester Township. 
STROPHOMENA MUSCULOSA Fenton 
Strophomena musculosa Fenton, Amer. Midland Nat., vol. 11, Nos. 3, 4, p. 153, pl. 8, figs. 1-7, 
1928. 
Types.—Holotype: Walker Mus. 25524; paratypes: Walker Mus. 25527, 
33421, 25525. 
Horizon and locality—Decorah formation (Ion member) in Minnesota: At 
Fountain, Goodhue County. 
STROPHOMENA OKLAHOMENSIS Cooper, new species 
Plate 260, A, figures I-10 
Shell small, wider than long, somewhat rectangular to semielliptical in out- 
line. Cardinal extremities varying from an acute angle to a right angle. Lateral 
margins variable, slightly oblique to perceptibly convex; anterior margin gently 
convex. Surface marked by costellae of unequal size. A single costella inter- 
calated between each of the primary costellae; one intercalated between each 
primary costella and the secondary one. This method of increase is continued 
on the entire surface. Intercalated costellae may grow to equal the primary 
costellae in strength. Consequently, the anterior parts of the valve do not show 
strong differentiation between the costellae; this is displayed on the posterior 
parts in varying degree depending on the individual specimen. 
Pedicle valve gently concave in the front half, flattened or concave anterior to 
the cardinal extremities depending on age; cardinal extremities moderately de- 
flected. Umbonal region narrowly convex, extended forward as a narrow but 
low fold nearly to the middle of the valve where the fold disappears in the 
general surface. Interarea very strongly apsacline; pseudodeltidium narrow, 
strongly arched. 
Brachial valve moderately convex with the maximum curvature at about the 
middle or slightly posterior to the middle. Umbo sulcate, sulcus narrow and 
moderately deep, extending nearly to the middle of the valve. Area surround- 
ing the sulcus flattened. Anterior and lateral slopes moderately steep; cardinal 
extremities not greatly deflected. 
Interior of pedicle valve with a nearly circular muscle field not quite extending 
to the middle. Floor of muscle field moderately thickened, and slightly elevated ; 
half enclosed by extensions from beneath the teeth. Median ridge low and short, 
extending about to the anterior ends of the diductor impressions. Teeth small. 
Subperipheral rim varying from obsolete (not developed) to moderately strong. 
Portion outside subperipheral rim narrow. Interior of brachial valve unknown. 
