THE KIMMSWICK AND PLATTIN LIMESTONES 
219 
Posteriorly a few specimens show traces of a prolongation of the 
shallow depressions backward in the form of almost obsolete 
dorsal furrows. The anterior part of the cranidium curves 
downward without any indication of a marginal concave curva- 
ture of the cephalon. Anteriorly the facial sutures meet at an 
obtuse angle; nevertheless this angle is sufficient to indicate 
that the facial sutures could not have been practically marginal. 
Pygidium convex as far as the posterior margin. Axial lobe 
almost or entirely obsolete. Antero-lateral margins curved 
abruptly downward along a distinctly angular ridge. Between 
this ridge and the antero-lateral angle, the slope is distinctly 
concave. Posteriorly, the margin of the pygidium is slightly 
angular rather than evetily convex. 
From the limestone immediately beneath the Buffalo or 
Maquoketa shales at the W. H. Benham locality, 3 miles south 
of Frankford, in Pike County. This limestone rests on the top 
of the typical Kimmswick, and is regarded as also of Mohawkian 
age. 
Compared with N ileus vigilans Meek and Worthen, from the 
lower Maquoketa of the upper Mississippi valley, the Trenton 
form here described, according to E. O. Ulrich (in a letter), 
has much less prominent eyes, larger palpebral lobes; the eyes 
situated farther from the anterior edge of the cephalon; the 
anterior outline of the cephalon is more uniformly rounded; 
the fixed cheeks are shorter; the front slope of the cranidium 
is less sharply deflected; the anterodateral angles of the crani- 
dium are less rounded; and the corresponding parts of the free 
cheeks, where they bend around the front of the cranidium, are 
narrower. 
40. Proetus undulostriatus Hall. 
A small cranidium, 3 mm. in length, was found at locality 2 
along Sanders. Creek, in Ralls County. It differs from typical 
Proetus undulostriatus from the Trenton (Snake Hill) of New 
York, chiefly in the greater distance between the anterior mar- 
gin of the glabella and the narrow anterior border of the cephalon. 
Moreover, the intervening part is distinctly convex, and at the 
