394 The American Geologist. june, 1892 



Section L^VIGATI. 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 striae. 

 Limb on the head disappearing; on the pygidium it becomes broad. 

 {Agnostus Icvvigatufi. Dalm., plate X, fig. 8). 



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 extremit}^, 

 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 ma}' be that of the genus 

 Microdiscus. 

 Locality. Oseola Mills, on tlie 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 



