682 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Pedicle valve moderately convex in lateral profile and with the maximum con- 
vexity at about the middle; anterior profile somewhat narrowed; median region 
somewhat narrowed but becoming flattened and faintly depressed in the anterior 
third. Beak long, narrow, incurved, Flanks faintly convex. 
Brachial valve only slightly less deep than the pedicle valve, fairly strongly 
convex in lateral profile and with the maximum convexity just posterior to the 
middle; anterior profile broadly and moderately convex ; region just posterior to 
middle strongly inflated; umbo swollen; anterior half flattened; flanks not dif- 
ferentiated from the median region, gently convex but with gentle slopes. 
Measurements in mm.—Holotype, length 2.8, width 2.5, thickness 1.6. 
Types.—Holotype: 117246a; unfigured paratypes: 117246b-1. 
Horizon and locality Whistle Creek formation in Virginia: On U. S. High- 
way 60, 100 yards southeast of Whistle Creek, 2 miles northwest of Lexington, 
Lexington (15’) Quadrangle. 
Discussion.—This species is characterized by its long beak, lack of folding, and 
absence of well-marked fold and sulcus. It differs from P. rotunda and P. micro- 
scopica, which it resembles in its strong convexity, by its general lack of folding. 
PROTOZYGA NICOLLETI (Winchell and Schuchert) 
Plate 141, J, figures 51-57 
Hallina nicolleti WINCHELL and ScHucHERT, Amer. Geol., vol. 9, p. 293, Apr. 1, 1892; Geol. 
Minnesota, vol. 3, p. 474, pl. 34, figs. 59-64, 1805. 
Zygospira aquila SARDESON, Minnesota Acad. Nat. Sci. Bull. 3, p. 335, pl. 4, figs. 15-18, 
Apr. 9, 1892. 
Z. nicollett Winchell and Schuchert, BEECHER and ScHUCHERT, Proc. Biol. Soc. Washington, 
vol. 8, pt. 2, p. 71, pl. 10, fig. 23, 1893. 
This is one of the largest of the known species of the genus and can be recog- 
nized by its strongly incurved beak, strongly elevated fold of the pedicle valve 
with narrow sulcus, strongly incurved beak, narrow brachial fold in a wide, 
shallow sulcus, and the strong and numerous costae marking the flanks. A large 
specimen measures 5.4 mm. in length, 5 mm. in width, and 3 mm. in thickness. 
The species differs from P. rotunda by its stronger costation and more promi- 
nent fold on the brachial valve. It differs from P. superba by its shallower sulcus, 
less pronounced fold on the pedicle valve and stronger fold on the brachial valve, 
combined with the less prominent beak. 
Types.—Figured hypotypes: 24201a, 49060a. 
Horizon and locality.—Platteville formation in Minnesota: At St. Charles, 
Winona County; Rochester, Elmira, and NW4 sec. 10, Olmstead County; Min- 
neapolis. 
Platteville formation (MacGregor member): On Minnesota Highway 74, 
just east of Chatfield; U. S. Highway 52, 2 to 3 miles north of Fountain, Fill- 
more County. 
In Illinois: 14 miles northeast of Dixon, Dixon (15’) Quadrangle. 
Same formation in Wisconsin: Road cut near Dickeyville, sec. 9, T. 2 N., 
