28 
MUSEUM BULLETIN No. 31* 
in haying the width at the hinge less than the greatest width and in 
haying a much higher cardinal area. The deltidium is also narrower. 
The most nearly allied form seems to he Clitambonites altissimus 
Winchell and Schuchert, a shell that has, however, a much wider 
deltidium. 
Genus, Zygospira Hall. 
Zygospira uphami Winchell and Schuchert. 
Plate VIII, Figures 1-5, 
Zygospira uphami Winchell and Schuchert. Am. Geo'l. 9, p. 291, Pal. 
Minn., 3, pt. 1, p. 468, PL 34, figs. 45-48. 
This species has not been identified previously outside of Min- 
nesota. It is so large and convex that it suggests Oatazyga, 
Description . Shell large for the genus, transversely oval in out- 
line, strongly bi-convex, with a low fold on the pedicle and a broad, 
shallow sinus in the brachial valve. Surface covered with fine 
radial plications, of which there are twenty-seven to thirty on each 
valve of a large specimen and about twenty on a small one. One large 
individual (12 mm. wide) has seven plications in the sinus and ten on 
each side on the brachial valve, and a email one (7 mm. wide) has six 
in the sinus and seven on each side of it. The smallest specimen seen 
(5 mm. wide) has four in the sinus and six on each side. The usual 
number in the sinus among adults is six. 
The largest specimen is 10 mm. (estimated) long, 12 mm. wide, 
and 7-5 mm. thick; an average one is 9-5 mm. long, 11 mm, wide, 
and 7 mm. thick; the smallest is 5 mm. long, 5 mm. wide, and 2-5 mm. 
thick. 
Horizon and Locality . Found 20 feet below the top of the Prosser 
limestone (Fusispira beds) near Spring Valley, Wykoff, and 
Fountain, Minn. In Ontario, fairly abundant in the lower part of 
the Collingwood at Oraigleith, Grey county, where it was collected 
by E. J. Whittaker and the writer. 
Class, Gastropoda. 
Genus, Hormotoma Salter. 
Hormotoma trentonensis Ulrich and Scofield. 
Plate VIII, figures 10, 11. 
Murchimnm bellicincta Hall, partim. Pal. New York, vol. 1, 1847, PI. 
39, fig. le. 
Hormotoma trentonensis Ulrich and Scofield. Pal. Minn., vol. 3, pt. 
2, 1897, p. 1017, PL 70, figs, 13, 14. 
For further references see Baaaler. Bull. 92, U.S. Nat. Mus., 
1915, p. 648. 
