736 THE PALEONTOLOGY OF MINNESOTA. 
[Note on Ceraurus. 
pairs of glabellar furrows are exceedingly obscure and may be discerned only in an 
oblique light. Occipital furrow narrow and deeply impressed; occipital ring broad 
in the middle, highly arched on the axis, which is scarcely as wide as the base of 
the glabella. On the cheeks the occipital ring gradually widens, at its extremity 
meets the outer marginal rim of the border, and is continued into a short, outwardly 
directed spine. The occipital furrow is also sharply defined upon the cheeks. 
Hyes of moderate size, not elevated to the hight of the glabella. Suture normal; 
ocular ridge from the anterior angle of the eye to the frontal margin broad and 
conspicuous. The entire surface of the shield is minutely and uniformly pustulose 
over all its parts. 
This species has somewhat the general aspect of Ceraurus pleurexanthemus, 
but differs from it characteristically in the obscure lobation of the glabella, the 
surface granulation, and the shortness of the genal spines. It is, I believe, wholly 
distinct from any of the various species “ Cheirurus” described by Billings from the 
Lower Silurian, though the usual imperfection of Billings’ material renders a decisive 
opinion impossible. 
Formation and locality.—Lower Trenton limestone, with Orthis pectinella and Strophomena subtenta, 
Minneapolis; and the Glades, Lebanon, Tennessee, Collection of Mr. Ulrich. , 
Note on THE SuBGENERIC CLASSIFICATION OF THE AMERICAN SPECIES OF THE GENUS 
CERAURUS. 
The wide variation in the form and degree of lobation of the glabella and form 
of the pygidium in species which have been referred to Ceraurus, led Angelin, 
Schmidt, and some others, to introduce a number of subordinate and useful 
designations for what appear to be natural groups. The structure of Ceraurus as 
exemplified by its type species, C. plewrexanthemus, is characterized by its subquad- 
rate glabella with moderately large frontal lobe, short, subequal lateral lobes 
separated by horizontal furrows, the third lobes being apparently isolated by a 
linear depression extending from the actual inner termination of the furrow to the 
occipital groove. The surface of the inner cheeks is characteristically marked by 
deep pittings scattered among the tubercles, while the pygidium bears two or three 
pairs of marginal spines, the first being of very great length. E 
The principal points. of deviation from this type are manifested in the compo- 
sition of the glabella. The glabella in Cyrtometopus, Angelin, Pseudosphaerexochus, 
and Nieszkowskia, Schmidt, is subtriangular, broadly clavate or subovoid, the lateral 
furrows and lobes being directed posteriorly. In Cyrtometopus the glabella is evenly 
and not greatly convex, and the third lobe is usually not wholly separated from the 
glabella. The ridge extending from the eyes forward to the anterior margin of the 
