FOSSILS OF TIIK ACADIAN GKOUP. 647 



the glabella, encroaching upon the marginal fold, causing it to be 

 thickest on each side of this prominence. 



The posterior margin is also folded, but the plait is more or less 

 inclined backwards. The fold is narrow near the occipital ring, but 

 grows moi'e prominent, and gains in width towards the posterior angle, 

 but, like the anterior fold, it disappears at that point. Its course is not 

 straight ; at about half the distance of the outer angle it bends slightly 

 backwards and downwards, and then forwards slightly, to disappear on 

 the flattened or rounded angle of the shield. This fold is separated 

 from the cheek-lobes by a groove shallower and broader than the mar- 

 ginal one, which it resembles, by expanding gradually into the flat- 

 tened space of the outer angle. This groove follows a course parallel 

 to the fold which it accompanies. Length from occipital furrow about 

 half that of head. 



Glabella sub-conical, longer than wide, strongly rounded in front, 

 and about half as wide anteriorly as posteriorly ; length about half that 

 of whole shield, strongly convex, but less elevated than the cheek-lobes, 

 bounded laterally and anteriorly by deep grooves, the anterior being not 

 so deep as the posterior. The sides of the glabella are impressed and 

 divided into lobes by three pairs of deep lateral glabellar furrows. 

 Those of the posterior pair are the longer and more deeply impressed. 

 These furrows begin abruptly at a point somewhat in advance of the 

 middle of the longer diameter of the glabella, and dii'ected back- 

 wards at an angle of about 45° to the antero-posterior diameter of the 

 shield, disappear abruptly without gaining the medial line, usually 

 extending a little more than the third of the distance across the gla- 

 bella. Those of the median pair begin also on the bounding groove 

 very abruptly, only a little in advance of the posterior pair, but they 

 are usually not so oblique, and extend on each side not more than a 

 quarter of the distance across the glabella. The distance between the 

 outer extremity of the median and anterior furrows is somewhat less 

 than between those of the median and posterior, and these but slightly 

 impress the sides of the glabella, and occasionally are scarcely visible. 

 The anterior lobe is about as wide as the one which follows it. 



The occipital furrow is deeply cut in the outer third of its length, 

 and strongly directed forwards. In the middle third it is not so deep, 

 and is quite strongly arched forwards. The occipital ring is narrow, 

 strongly convex, and vertically arched, the sides being more or less 

 narrowed, turned downwards and forwards, being projected obliquely 

 more or less across the posterior marginal cheek-groove towards the 

 inner posterior angle of cheek-lobe. The ring projects backwards beyond 

 the margin, but not beyond the posterior lateral angle of shield. The 



