Potsdam of Wisconsin and Lake Superior. [229] 5 
of all superficial ornaments. But three whorls have been seen; 
these are *66 inch in height, and the lower one is about *77 inch 
in diameter—the three being of nearly equal height. 
This fossil is quite unlike anything described from the Pots¬ 
dam sandstone; and there is nothing in the Calciferous sand- 
rock which approaches nearer than Holopea Proserpina Billings 
(Pamphlet, Jan. 1862, p. 28), with which this may be congeneric. 
Dicellocephalus Minnesotensis, Owen. 
Several specimens occur in the collection which I feel obliged 
to refer to this species. Some well preserved pygidia do not 
disagree with Owen’s and Hall’s ( Foster and Whitney's Pep. on 
L . Sup. Land Dist ., pi. xxiii, fig. 80) figures, except that Hall’s 
specimen had lost its caudal flap—a feature well preserved in 
my specimens, and distinctly reflected upward. Nevertheless, 
no caudal spines are preserved in any case; and the condition 
of the specimens would indicate that they were wanting. An 
imperfect cephalic shield presents a flat border, about as wide as 
the caudal flap, and, like it, turned slightly upward, and is desti¬ 
tute of a thickened margin. The glabella is truncately rounded 
in front; the two sides are nearly straight, but not perfectly 
parallel—being approximated anteriorly at an angle of about 
12°. There is at least one furrow extending across the glabella; 
and in front of this, opposite the anterior extremity of the pal¬ 
pebral lobes, another furrow on each side, reaching less than 
one-third the distance transversely across the glabella. The 
course of the great suture in its anterior extension conforms to 
the requirements of this species. 
A doubt may exist whether these specimens are correctly re¬ 
ferred, in consequence of the absence of the caudal spines and 
the defective condition of the posterior portion of the cephalic 
shield. It seems to me, however, that a pair of blunt spines, in 
an attenuated peripheral part like the caudal flap, cannot form 
an indispensable diagnostic character. The direction of the 
facial suture is exactly that of D. Minnesotensis; and the inclina¬ 
tion of the sides of the glabella, even if slightly greater than is 
usual for this species, is not as great as in D. misa Hall. The 
pygidium conforms, in its want of spines, to that of D. misa , but 
the configuration of the glabella and the anterior lobe of the 
fixed cheek deviate decisively from that species. 
Dicellocepijalus Pepinensis, Owen. 
An imperfect cephalic shield shows a narrow border, with a 
decidedly thickehed margin, which is broader than the furrow 
between it and the front of the glabella. The glabella is prom¬ 
inent, with sub-parallel sides and an obtusely rounded anterior 
extremity. Opposite the middle u of the prominent palpebral 
