324 
Aug. F. Foerste 
Ohio. There it is listed by John M. Nickles from the Corryville 
horizon. The glabella is rotund oval, without visible lobation. 
The border of the cephalon is broad and flat, even anteriorly, 
and defined from the remainder of the cephalon by its more 
nearly horizontal slope as well as by the shallow groove; there is 
no additional narrow elevation along the margin of the border. 
Thoracic segments comparatively prominent. Pygidium with 
prominent axis, and flat lateral lobes having a plain expanded 
border; lateral lobes with about four indicated segments, becom- 
ing indistinct posteriorly, the first two with longitudinal furrows. 
In Proetus chambliensis the glabella is relatively longer and more 
oblong oval in outline. It presents not only fairly distinct indi- 
cations of the large basal lobes, but also indications of the middle 
pair, the limiting furrows being readily distinguishable under a 
lens. Along the outer margin of the flat border of the cephalon 
there is a very narrow elevated line, which becomes broader and 
more prominent just before reaching the anterior part of the 
facial suture, and which gives rise to the strongly defined mar- 
ginal elevation of the cephalon at the edge of the border ante- 
rior to the glabella. The eyes are relatively longer and more 
closely appressed to the glabella. The thoracic segments are 
less prominent, especially along the axial lobe. The axial lobe 
of the pygidium rises strongly above the very moderately convex 
lateral lobes, and only the anterior segments are distinctly indi- 
cated. While unquestionably closely related to Proetus parvius- 
culus, it seems possible to distinguish the Canadian forms for the 
reasons indicated. 
52. Byssonychia carinata, Goldfuss 
{Petrefacta Germaniae, vol. II, p. 136, pi. 119, Fig. 8.) 
From the single figure accompanying this description it is evi- 
dent that the form is a species of Byssonychia. Twenty- two 
plications are indicated between the posterior margin and the 
abrupt descent of the umbonal ridge at the anterior face; possibly 
5 more plications belong to the anterior face, making a total of 
27 plications, as figured. The original specimen may have had 
more, especially toward the posterior margin of the hinge-line. 
The general outline of the shell is not rotund but obliquely 
quadrate oblong with the greater axis in an approximately vertical 
