BRITISH FOSSILS. 



5 



length of the head ; it is narrow, oval, and nearly all occupied by 

 the swelled central lobe, the two linear oval lateral lobes on each 

 side, and a minute upper third one, only skirting the base of the 

 large central one, and not indenting its sides, as they do in most 

 other species. In front, this protuberant lobe pushes forward the 

 anterior margin and makes it sinuous, and behind it is immediately 

 succeeded by the two short diverging neck spines (with a small 

 tubercle between them), no space being left for a large neck seg- 

 ment. The cheeks are roundish, rather convex, and steeply bent 

 downwards, as shown in our lowest figure, which is a section of 

 the head; they have a thickish border separated by a strong 

 furrow, and studded on the edge by several small spines, and they 

 are enlarged outwards so as to overhang the base of the stout spine 

 which occupies the posterior angle. Between the projecting anterior 

 margin of the cheeks and the equally projecting front, the border is 

 depressed on each side of the glabella, so as to form a hollow curve 

 in which the facial suture terminates. The posterior margin of the 

 cheeks is uneven, and shows a slightly impressed neck furrow. The 

 eyes are apparently large and prominent, with a tubercular eye lobe, 

 and are placed full half-way up the cheek, and about half-way out- 

 ward, or rather more, from the convex lobe of the glabella. Between 

 the eye and the small glabella lobes, and parallel to the latter, the 

 space is filled up by a longitudinal swelling or lobe, rising above the 

 surface of the cheek, but fused with it towards its prominent base. 

 An oblique ridge below the eye connects that organ with the stout 

 widely diverging cheek spine, and along this ridge the facial suture 

 runs, and is supposed to terminate just within the base of the spine, 

 but the head could not have been separated at the facial sutures. 

 Coarse tubercles, with a few finer ones, cover the whole of the head 

 except the shallow furrows ; they are not, however, distinct on the 

 cheek border, nor on the ocular ridges. 



Affinities. — Now that we have a perfect head of this species, there 

 is no other with which it could be confounded. The figure given by 

 Professor M'Coy, cited above, is quite correct, but it was from a 

 very fragmentary specimen, and both he and myself regarded the 

 first found specimens of A, Jamesii as identical with it. That 

 species, however, as contrasted with small and more perfect speci- 

 mens we now possess, difiers by its depressed form, and by its lobed 

 glabella, with the median lobe moderate as compared with the side 

 ones. In this species it is monstrously developed at the expense of 

 the others, which are reduced to mere rudiments. The eyes, too, lie 

 more outwards and forwards, and in this as weU as the gibbosity 



