708 THE PALEONTOLOGY OF MINNESOTA. 
UIsotelus suse. 
are not impressive. The smaller individual has a more decidedly flattened cephalic 
border than the larger, but this difference is probably due to circumstantial causes; 
its cheek spines are much the longer, extending to the sixth segment, while on the 
larger example they reach only to the second. 
Formation and locality.x—Lower Trenton; Fillmore county, and Stanton, Goodhue county. 
IsoreLus sus# Whitfield, 1882. 
Asaphus suse (GALVIN in MS.) WHITFIELD, 1882. Geology of Wisconsin, vol. iv, p. 236, pl. 5, fig. 3; 
pl. 10, fig. 8. 
The features distinguishing this form from its allies in the same fauna lie mainly 
in the general proportions of the animal. Both cephalon and pygidium are broad 
and relatively short, their outlines being in contradistinction to the elongate and 
subangular head and tail shields of J. gigas and I. maximus. In addition, there is a 
general and very regular convexity of the parts, a sharper definition of the thoracic 
axis, deeper and more distant axial furrows on the pygidium; the facial sutures, also, 
on their anterior limb, make broad, sweeping outward curves and a large angle at their 
union. The description of the species has been given in detail by Mr. Whitfield in 
the work cited and it is only necessary here to indicate the differential characters. 
Figs. 10, 11. Two views of an imperfect, partially enrolled individual of Jsotelus susce Whitfield. 
Formation and locality.—Specimens having about the same dimensions as the original occur in the 
Hudson River group at Granger (Museum No. 8434) and two miles east of Spring Valley. Minn. (collection 
of Mr. Ulrich). 
