996 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Discussion.—This species differs from P. circularis in its more convex valves, 
proportionately wider hinge, and somewhat stronger costellae. It differs from 
P. subaequata in having finer and more even ornamentation and narrower hinge. 
PIONODEMA UNIPLICATA Cooper 
Plate 154, F, figures 25-33 
Orthis (Dalmanella) subaequata var. gibbosa WINCHELL and SCHUCHERT (not O. gibbosa 
Billings), Geol. Minnesota, vol. 3, pt. 1, pl. 33, figs. 43-45, 1895. 
Pionodema uniplicata Coorer, Journ. Paleont., vol. 4, No. 4, p. 379, pl. 35, figs. 1, 2, 1930.— 
SCHUCHERT and Cooper, Mem. Peabody Mus. Nat. Hist., vol. 4, pt. 1, pl. 23, fig. 12, 1932. 
This species was created for Pionodemas having a strong fold and sulcus. 
Types.—Holotype: Y.P.M. S1358; figured hypotypes: U.S.N.M. 86571, 
117341, 117342. 
Horizon and locality—Decorah formation (Spechts Ferry—Ion?) in Minne- 
sota: At Chatfield and Lanesboro, Fillmore County ; Fountain, Goodhue County ; 
St. Paul; Minneapolis; Elmira, Olmstead County. 
Decorah formation (Spechts Ferry member) in Wisconsin: At Platteville, 
Mineral Point (30’) Quadrangle. 
Same formation in Iowa: 4 miles east of Waukon, Allamakee County. 
Platteville formation ? in Wisconsin: At Janesville, Rock County. 
Discussion—This species is characterized by its strong fold and sulcus, fea- 
tures that are not usual in the genus. Pionodema uniplicata is a homeomorph 
of Doleroides gibbosus, and the two occur together in the Spechts Ferry mem- 
ber of the Decorah formation. Specimens of Pionodema with strong fold com- 
ing from post-Spechts Ferry horizons may be aberrant forms of other species, 
but the limited representation of the species in the National Collection will not 
permit definite determination of this point. 
PIONODEMA sp. 1 
Plate 154, G, figures 34-40 
Shell small, wider than long, subquadrate to subcircular in outline; hinge nar- 
row ; sides and anterior margin rounded. Costellae strong, numbering about 3 
to the millimeter at the front margin. 
Pedicle valve deeper than the brachial valve, strongly convex in lateral profile ; 
anterior profile strongly arched and with steep lateral slopes ; umbonal and median 
regions strongly swollen ; anterior slope steep. Interior with long, strong, flaring 
dental plates surrounding the sides of a wide muscle field. Apical plate well 
developed. 
Brachial valve moderately convex in lateral and anterior profiles; umbo sul- 
cate, sulcus short and shallow; median region swollen; lateral slopes short and 
moderately steep. Interior with stout brachiophore plates flaring moderately, 
their anterior ends extended at an angle toward the median ridge. Shaft of 
cardinal process short; myophore small. Median ridge narrow, elevated, promi- 
nent, extending anterior to the middle. 
