25 



axis obscurely indicated, quite obsolete at two-thirds the length ; side-lobes 

 Avith a few obscure indications of lateral furrows. 



Length of the largest specimen collected 31 lines ; width at the fourth 

 pleura about 20 lines ; length of the head from the front to the posterior 

 margin in a straight line 10 lines ; length of the same following the curve 

 12 lines ; width at the base of the spines 23 lines ; length of the thorax 12 

 lines ; length of the pygidium Hi lines ; width of the same 18^ lines. 



Fig. 8. 



Fig. 8. — Asaphus notans. — A specimen from English Head. 



The specimen figured (which is intended to be the type) has the crust 

 removed from the greater part of the head and the eyes broken off. 

 But another specimen about 18 lines in length has the head perfect with 

 the exception of the posterior angles of the cheeks. It was found in the 

 same locality with the large one, and appears to be certainly the same 

 species. The eye of this specimen is truncato-conical, rising vertically (to 

 the horizontal plane of the body) to the height of a little more than one line ; 

 the summit is irregularly rounded, most elevated near the posterior side ; 

 on the inside the surface slopes with a gentle curve, and gradually merges 

 into the general surface. Examined microscopically the visual surface is 

 seen to be smoooth and transparent, showing, beneath, a vast number of 

 lenses arranged in both vertical and oblique hues. The facial suture in 

 proceeding from the eye to the front margin has the usual sigmoid curve, 

 but for about one-half its course in the middle of the margin it runs along 

 the extreme edge ; not a little within the edge as is usual in species of this 

 genus. The surface is apparently smooth, but when magnified seems to be 

 obscurely wrinkled. Length of the head in a straight line a little more 

 than 5 lines ; length of the thorax 6 lines ; length of the eye about IJ Imes. 

 The anterior angles of the eye are at the mid-length of the head, and the 

 posterior about 1 line from the margin. 



