183 



If a line be drawn across touching the posterior edge of the neck-segment, 

 the contour in front of that line is nearly a perfect semi-circle. Glabella 

 regularly conical, its length about five-ninths that of the head ; posterior 

 furrows distinct, entering at about one-half the distance from the ocular 

 ridge to the posterior margin of the neck segment, thence running obliquely 

 inward and backwards at an angle of about 45, apparently not quite one- 

 third the width ; two anterior furrows on each side, represented by obscure 

 pits ; neck furrow narrow ; neck segment convex, strongly elevated on the 

 fixed cheeks. The eyes are small, and situated on a line drawn across the 

 glabella at the anterior fourth; ocular ridge well defined, smooth, pro- 

 longed, with a backward curve outside of the eye. Thorax a little more 

 than half the width of the head ; the axis strongly convex and gradually 

 apering backwards ; side lobes flat ; pleurae with a wide groove along the 

 middle, a small portion of their outer extremities turned backward. Sur- 

 face of thorax, glabella, and a sub-reniform space on each side of the base 

 of the glabella, smooth ; the border with circular punctures about one-tenth 

 of a line in width, and separated by smooth rounded interspaces half their 

 own width ; the punctures larger and more distant at the inner edge of the 

 border; on the elevated part of the cheeks they have a sub-reticulated 

 arrangement. 



Length of the head, including the border, 8J lines ; width at neck- 

 segment, 16 lines ; length of glabella 5 lines; width of the same at the 

 base 4 lines ; length of the posterior prolongations of the border behind a 

 line drawn across at the neck-segment 9 lines ; distance of the eye from 

 the side of the glabella 1 line. 



The crust on all the middle part of the glabella is broken away, but the 

 part of it which remains on the side is smooth even when viewed through 

 a pocket lens. 



Harpes Dentoni has the surface differently marked, the eye more distant 

 from the glabella, and the lateral spines proportionally longer. 



Locality and Formation. City of Ottawa ; Trenton limestone. 



Collector. Dr. J. M. Grant, Ottawa. 



HARPES DENTONI. (Billings.) 



Fig. 166. 

 (Canadian Nat. and Geo. ; vol. 8, p. 36: 1863.) 



Description. The head of this species, exclusive of the posterior pro- 

 longation of the border, is nearly semi-circular. The border itself is not 

 wholly preserved in the specimen, so that its width cannot be ascertained. 

 The length of the head without the border is six lines, and its width on a 



