422 ME. JP. E. COWPEE EEED OK" THE [Aug. 1 896, 



The second lateral - furrow is situated halfway between the first 

 and third lateral furrows. Like the first, it is curved gently back- 

 ward and is faint and narrow. It does not exceed the first in 

 length, and runs parallel to it. 



The third side-farrow is much stronger and deeper, and curves 

 more strongly backward towards the neck-furrow. It does not, 

 however, reach the latter, and only a weak groove even in the casts 

 appears to connect the two. The basal lateral lobes thus defined 

 are rhomboidal in shape, do not rise above the general convexity 

 of the glabella, and are separated by an interval equal to their own 

 width. 



The axal furrows are distinct and well marked, but not so broad 

 as in Ch. (Ps.) conformis. The neck-furrow is stronger and broader 

 than the axal furrows, and curves forward in the centre at the base 

 of the glabella. The neck-segment is rounded, and has a width 

 equal to about half the length of the basal lobes of the glabella. 



The cheeks — the fixed portion is alone preserved in the Keisley 

 specimens — bend down steeply on each side, with a convexity from 

 back to front, and are scarcely at all elevated. The furrow marking 

 off the neck-ring is distinct, and curves forward at the genal 

 angle to pass into the broader marginal furrow. The genal angle 

 is produced into a short, triangular spine, backwardly and slightly 

 outwardly directed. The width of the cheek is considerably less 

 than one-third of the total width of the head-shield, and this is a 

 marked and important feature. 



The anterior branch of the facial suture cuts the front margin of 

 the head-shield nearly at the level of the first lateral furrow of the 

 glabella, and thence runs backward parallel to the axal furrow of 

 the eye. The posterior branch curves outward and backward from 

 the eye, at first nearly parallel to the posterior margin, to cut 

 the lateral margin a short distance in front of the base of the genal 

 spine — nearly at the level of the third lateral furrow of the glabella. 



The small eye is situated opposite to the second lateral lobe of 

 the glabella, and approximately on the highest portion of the cheek. 

 The eye-lobe rises up steeply from its base, and is there separated 

 from the surface of the cheek by an oblique groove. 



There is a broad and short ' frontal limb ' in front of the glabella 

 as figured by Schmidt (op. cit.) in Ch. (Ps.) hemicranium. 



The whole surface of the head-shield is ornamented with small 

 tubercles, not closely set, and the cheeks have in addition small 

 pittings. 



The points of difference between this form and Ch. (Ps.) hemi- 

 cranium are : (1) the greater breadth of the glabella in proportion 

 to the head-shield ; (2) the smaller breadth of the head-shield ; 



(3) the subquadrate shape and greater convexity of the glabella; 



(4) the more forward position of the point of section of the lateral 

 margin by the facial suture. In all other points the two species 

 seem to agree very closely. 



In size the Keisley form is about double that of any of the Eussian 

 specimens of Ch. (Ps.) hemicranium. One of our head-shields of 



