280 
Aug. F. Foerste 
cardinal ridge. Even the lower part of the posterior termination 
of the shell, above the umbonal ridge, is occupied by oblique pli- 
cations. Transverse plications vary in number from 10 in a 
length of 10 mm. near the anterior part of the shell to 6 in the 
same length posteriorly. Length 66 mm., height posteriorly 
31 mm., height at beak 20 mm., possibly shortened here by com- 
pression. Anterior margin extending 10 mm. anterior to the 
beak, convexity of the single valve about 7 mm. 
Locality. Riviere des Hurons, near St. Jean Baptiste; col- 
lected October 1872 by Thomas Curry; forming specimen No. 
2Q71, Paleontological Collections, Geological Survey of Canada, 
Victoria Memorial Museum, Ottawa, Canada. 
The chief characteristics of the form here described are its 
shorter length, its greater convexity, and the more pronounced 
forward curvature of the low transverse plications. If these 
characteristics do not prove fairly constant, when numerous speci- 
mens from the same locality are collected, this form has no stand- 
ing whatever, even as a variety. 
The chief reason for describing the preceding specimen is the 
fact that this gives an appropriate opportunity to discuss the 
form described by Hall and Whitfield as Sedgwickiaf divaricata. 
Although the type of this species should occur in the U. P. James 
collection, at Chicago University, it is unknown there. It was 
found in the shales of the Richmond group at Blanchester, Ohio. 
A mile northwest of Blanchester, where the north and south road 
crosses Second Creek, the lowest exposures belong to the lower 
Hebertella insculpta horizon, at the base of the Blanchester divi- 
sion of the Waynesville, but there is good collecting from here 
westward down the stream. Knowing this area very well, I 
am of the opinion that if ever the type of Sedgwickia divaricata 
is found it will prove to be a young specimen belonging to the 
Whiteavesia pholadiformis group. In young specimens of this 
species the basal margin is convex, and the umbonal ridge is fairly 
angular. Moreover, the concentric markings sometimes are fairly 
conspicuous on the cardinal slopes, and would be especially con- 
spicuous on specimens in which these concentric markings were 
conspicuous below the umbonal ridge. Judging from the figure 
of Sedgwickia divaricata published in vol. ii of the Palaeontology 
of Ohio, the type specimen presented the low broad plications 
curving from the posterior margin of the shell obliquely forward 
