830 



The cheek angles are rounded, and the posterior margin of the head 

 makes with the lateral lower margin, as seen in a side view, usually a 

 right angle, but in some specimens an obtuse angle of nearly 100*^, owing 

 to the variable extent to which the front part of the head is produced 

 downwards. In some the portion of the posterior margin outside of the 

 eye curves forwards, and brings the cheek angle to a position in front of 

 the eye. In others, it is behind the eye. The space between the eye and 

 the dorsal furrows is convex, and the eye itself seems to be rather strongly 

 protuberant or sub-conical. The movable cheek is sub-triangular, its 

 width at the posterior margin about one and a half the distance of the eye 

 from the dorsal furrow, its length along the lower margin a little greater 

 than its posterior width. The anterior margin of the whole head is uni- 

 formly rounded, with the exception of a slight concave curve just outside 

 of the suture. In some specimens in which the front part of the head is 

 most abruptly bent down the middle portion of the fi-ont margin is 

 depressed convex or nearly straight. 



Thorax with ten segments. Axis moderately convex, from a little more 

 than one-third to nearly one-half the width of the whole animal, a little 

 wider at the anterior than at the posterior segment ; the sides sometimes 

 straight, and sometimes slightly curved outwards. On each side of the 

 axis there is a flat space between the side of the axis and the bend of the 

 pleurae. The width of this space is between one-third and one-half the width 

 of the axis. The pleurae are bent at the fulcra at an angle which varies 

 in diflerent individuals, from 25° to 45°, and at nearly one-half their length 

 from the side of the axis. 



Pygidium usually a little shorter than the thorax ; varying from moder- 

 ately to rather strongly convex ; the posterior margin broadly and uniformly 

 rounded ; the anterior angles truncated nearly half the whole length of 

 the pygidium ; the straight sides formed by the truncation forming an 

 angle of from 40° to 60° with the longitudinal axis of the body. The 

 axis of the pygidium is well defined at the anterior margin by the dorsal 

 furrows, which die out at about one-third or one-half the length, converging 

 towards each other, and sometimes obscurely defining the apex. 



The surface characters of this species are peculiar, although somewhat 

 variable. The specimen on which the species was originally founded has 

 the whole of the head and pygidium covered with short sqaumose fissure- 

 like striae ; one edge of each fissure, being more elevated than the other, 

 gives to the surface a wrinkled appearance. These striae vary in length 

 from half a line to two or three lines, and are from one-eighth to one- 

 fourth of a line distant from each other. On the tail they seem to radiate 

 irregularly from the axis as a centre. Near the front margin and parallel 

 with it, arc a number of straight continuous fissures. This latter character 



