MEDINAN, NIAGARAN, AND CHESTER FOSSILS 
53 
4. Whitfieldella circular is Sp. nov. 
Plate XIII, figs.X A, B 
Cf. Atrypa oblata Hall, Pal. New York, 2, 1852, p. 9, pi. 4, 
figs. 4 a, b, c, and 5. Cf. Whitfieldella cataractensis Williams, 
Geol. Surv. Canada, Memoir 111, 1919, p. 121, pi. 7, figs. 16, 
17, 18. 
One brachial valve (fig. 8 A) is 11.3 mm. long, 10.5 mm. wide, 
and 3 mm. deep. It is quite evenly convex, except at the margins 
where it curves more rapidly. Concentric lines are seen near 
these margins. A median septum in the interior of the valve 
extended about 3 mm. from the beak. 
A second brachial valve (fig. 8 B) is 9.3 mm. long, 9.2 mm. 
wide, and 2.3 mm. deep. The median septum on its interior is 
2.5 mm. long. 
These valves do not appear to be the young of Whitfieldella 
oblata (Hall), from the Upper Aledinan of Lockport, New York. 
The first of the two specimens here described appears quite 
mature, judging from its convexity along its margins. Nor is 
it identical with Whitfieldella cataractensis Williams. 
5. Modiolopsis orthonota creditensis Var. nov 
Plate XIII, figs. 1, 2 A-G 
Modiolopsis orthonota. Pal. New York, 2, 1852, p. 10, pi. 4 
(bis), figs. 1 a-c. 
Numerous valves, of which the largest is 21.5 mm. long, 10.6 
mm. high, and 2.5 mm. deep. Specimens 16 to 18 mm. long 
are much more common. The cardinal and ventral margins 
tend to converge posteriorly. In one specimen 18 mm. long, 
the height of the specimen at the beak is 9 mm., while 10 mm. 
posterior to the beak it is 8 mm. in height. This appearance of 
convergence posteriorly is due in part to the rise of the umbonal 
part of the valves above the hinge-line. The posterior part of 
the ventral margin rises convexly as far as the posterior termina- 
tion of the umbonal ridge, and from this point the posterior 
margin of the valve curves strongly forward at an angle of about 
