Vol. 52.] FAUNA OF THE KEISLET LIMESTONE. 415 



of that of the general surface of the middle shield and of that of 

 the fixed cheeks above which it rises. The convexity of the glabella 

 is continued in front of the free termination of the axal furrows up 

 to the summit of the middle shield, where it is lost. 



The axal furrows are distinct, of moderate depth and breadth, 

 have a curved course, and bend slightly outward at both their ends, 

 though more strongly posteriorly. They extend up about two- 

 thirds of the posterior slope of the middle shielJ. 



Each of the fixed cheeks is at its base nearly as wide as the 

 glabella, and, owing to outward curvature of the facial suture from 

 the posterior margin, it rapidly increases in width forward as far 

 as a point a little in front of the anterior end of the axal furrows. 

 Here it has a width twice that of the glabella. The fixed cheeks 

 fall down steeply and abruptly at their base to the narrow neck- 

 segment. 



There is no trace of an eye-lobe, and the species must have been 

 blind. 



The facial sutures cut the front margin at a distance from each 

 other of about twice the width of the glabella. Each suture curves 

 strongly outward and backward to the level of the front end of 

 the glabella, behind which level it runs backward and inward, at 

 first in a convex outward course and then with a slight inward 

 curve, so as to cut the posterior margin at a distance from the axal 

 furrow nearly equal to the width of the glabella. 



The front margin of the middle shield is furnished with a distinct 

 marginal furrow which marks off a narrow, raised, rounded border. 



The free cheeks are not preserved ; but, judging from the curvature 

 of the front margin, the course of the facial suture, and their shape 

 in allied forms, they must have been long and narrow. 



The whole surface of the middle shield is ornamented with very 

 closely-set puncta. 



Measurements of two Specimens. 



I. II. 



millim. millim. 



Length of middle shield 240 18-0 



Greatest width of do 355 25-0 



Greatest height of do 15-0 90 



Length of glabella (to end of axal furrows)... 130 7"0 



Width of do. at base 110 8-0 



Greatest width of fixed cheek 195 120 



(At a level a little in front of the anterior end of the glabella.) 



Note. — There are several smaller specimens not quite so much 

 elevated in the centre of the middle shield as those above described. 

 But in all other respects they agree with them completely, and 

 must be considered, at any rate for the present, merely as young 

 individuals or a variety of the same species. 



Illcznus galeatus is a very common form at Keisley. There are 

 specimens of it in Prof. Harkness's collection at Carlisle, but it is 

 labelled III. Davisi. There are numerous excellently preserevd 



