Trof, Hall on a New Crustacean, 445 



thickened border ; the posterior angles rounded. The margin is 

 impressed or sinuate in front, and there are slight indications of 

 longitudinal grooves on each side of the central, leaving a median 

 lobe proportionally wider than in Limulus. The eyes, though 

 imperfect, remind one somewhat of the eyes of Trilobites, and are 

 remarkably prominent. 



Carapace of jlglaspis from Wisconsin. 



There is a single fragment of what appears to have been an ar- 

 ticulation of the thorax, or a portion of some appendage analogous 

 to the branchial feet of Limulus ; it has a flattened, curving, point- 

 ed extremity. Another fragment I infer may have been the cau- 

 dal extremity ; it is comparatively thick and strong ; but the spe- 

 cimen is too imperfect to be determined. The first specimen I 

 obtained is a straight spine-like body, and I infer that the animal 

 may have been provided with a caudal spine, as in Limulus. 



Such, in general, are the characters of this crustacean. Whether 

 this may have been the animal which made the peculiar tracks in 

 the sandstone, I cannot say, but I have so inferred. The first speci- 

 men was found at a distance of thirty miles or more in a north- 

 westerly direction from the locality of the tracks of Black River, 

 and in higher beds of the sandstone. The last found specimens 

 are from a more distant locality, in a southeasterly direction, and 

 also from beds above those of the tracks. All this, however, can- 

 not furnish matter for argument against the origin of the tracks, 

 in the present state of our knowledge of a country which has 

 been comparatively but little exj)lored. 



Whatever may be proved hereafter in this respect, it does not 

 diminish the great interest attaching to so new and remarkable a 

 form of crustacean from the unequivocal primordial zone of the 

 northwest. 



