394 The American Geologist. June, 1892 
Section LEVIGATI. ‘The dorsal grooves marking the glabella 
and axis of the thorax and pygidium, are wanting or faintly indi- 
cated. Crust smooth, sometimes with slight indications of striz. 
Limb on the head disappearing; on the pygidium it becomes broad. 
(Agnostus levigatus. Dalm., plate x, fig. 3). 
AGNOSTUS DISPARILIS Hall, 1863. Plate x, fig. 15. 
Diagnosis, —Head semi-elliptical, convex towards the posterior 
side, and abruptly sloping in front; length and breadth nearly as 
3 to 4, a little concave on the posterior margin and marked near 
the edge by a narrow groove on each side of the middle; the centre 
slightly elevated close to the margin. The limb is a little wider 
in front than at the sides. The pygidium (?) is a little wider than 
long. The trilobation extends nearly to the posterior extremity, 
and is separated from it only by a narrow border. The axis is 
fully once and a half as wide as the side lobes, somewhat flattened 
on the summit, and very distinctly limited by the dorsal furrows. 
The pygidium figured with this species may be that of the genus 
Microdiscus. 
Locality. Oseola Mills, on the St. Croix river, Wisconsin. 
AGNOSTUS PARILIS Hall, 1863. Plate x, fig. 4. 
Diagnosis. —Head semi-elliptical; length and breadth about 
equal, very convex in the posterior part, and curving downwards 
to the anterior margin. The central portion of the posterior part 
is limited by a faint curving groove; and anterior to its limits 
there is a slight elevation, which may have a node on the surface 
of the crust. The posterior margin, just within the angles, is pro- 
duced in a minute node. The limb gradually expands from the 
posterior angles to the front, where it becomes well defined. The 
pygidium is slightly truncated at the anterior angles, the marginal 
rim narrower towards the articulating border. The central part 
is slightly more elevated and limited by furrows diverging from 
the anterior margin. On the median line, at a point $ the length 
from the front margin, there is a distinct elongated tubercle. 
Locality. Shores of lake Pepin. 
AGNOSTUS PROLONGUS Hall and Whitfield, 1877. Plate x, fig. 10. 
Diagnosis. —Head elongated, or very high dome-shaped in out- 
line. Surface depressed, convex in front and gradually rising to 
near the occipital border, where it becomes low, tumid. Glabella 
