182 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



anterior to the centre of the carapace. Near the posterior 

 margin of the central division, there are two small pustules. 



Several fragments of thoracic articulations have been obtained : 

 these are all recurved, in greater or less degree, at the extremities, 

 without furrows upon the surface. A single segment remains ap- 

 parently entire : it is highly arched, having an elevation nearly 

 as great as the distance of the extremities. This segment is pro- 

 bably from the posterior part of the body. 



A single spine, three inches in length, and a fragment of an- 

 other similar one, have been obtained. The texture is everywhere 

 minutely punctate, and the surface minutely pustulose. 



Fig. 7, is the largest carapace obtained : one side is imperfect, and the opposite angle 

 broken off. The outline on the left is carried out from other specimens, 

 where that part is entire. 



Fia. 8, is a smaller carapace, not entire in front ; and the centre of the anterior margin 

 is covered by a bit of crust from some other part, or some other individual. 

 This specimen shows the pustules on the posterior margin of the carapace. 



Fig. 9, is the inner side of a portion of a small carapace, showing the cavities of the 



eyes. 

 Fig. 10. An enlargement of the surface, showing the texture. 

 Fig. 11. A segment of the body? probably from the posterior part of the animal. 

 Figs. 12, 13 & 14. Parts of segments? showing the characters of the extremities. 

 Fig. 15. A portion of a caudal spine of this animal. 

 Fig. 16. Another specimen of the same appendage. 



These remains occur in the upper portions of the sandstone ; and thus 

 far the specimens have been derived from two localities, one near Miniska 

 in Minnesota, and the other near Mazomania in Wisconsin. 



This new and remarkable Crustacean is of great interest, since 

 I believe no well-authenticated forms of this class, other than 

 Trilobites, have been found so low in the series of formations. 

 This fossil, moreover, if its relations be such as I have supposed, 

 is of great interest considered in connexion with the Tracks in 

 the Potsdam sandstone, which occur both in Canada and Wiscon- 

 sin. Whether any relation may exist betw^een the two, remains 

 yet to be proved by farther discoveries of specimens, and also of 

 the locomotive appendages which we may infer that this animal 

 possessed, in character not entirely dissimilar to those of Limulus. 



