170 PROCEEDINGS OF THE 



The sides of the ghil)ella are nearly parallel, and its surface 

 divided by three equidistant furrows, of which the anterior is shal- 

 lowest (sometimes almost invisible), shortest, and most transverse. 

 The middle one — that bounding the ocular lobe in front— is better 

 marked, directed slightly backwards, and occupying on either side 

 about one-third of the transverse breadth of the glabella ; the pos- 

 terior pair of grooves, marking off the basal lobes, leave one-fourth 

 of the glabella as a median ridge. They are deep, and after pass- 

 ing directly inwards, curve abruptly backwards, parallel to the axis, 

 towards the cervical fold, from which they are separated by a 

 narrow neck. The deep cervical fold lies in front of the cervical 

 ridge, whose breadth is one-seventh of the length of the head. 



The fixed cheek is equal in antero-posterior dimensions to the 

 basal and cervical lobes; its anterior margin is in line with the 

 posterior of the three furrows, and its gently arched surface is well 

 marked off by a slight longitudinal depression from the prominent 

 glabella. The outer margin is not straight, but bends slightly in- 

 wards posteriorly; the greatest width is, therefore, where it joins 

 with the free cheek. The posterior angle is produced into a spine, 

 which rapidly tapers in its proximal fourth, and thence continues 

 of nearly the same width. The posterior margin of the cheek slopes 

 obliquely outwards and backwards to the angle; it is raised, having 

 in front of it a groove continuous with the cervical groove. The 

 spine itself is directed outwards, so as to form an acute angle with 

 the axis of the body, and is curved, so that its convexity is dorsal, 

 and the tip does not descend below the level of the under edge of 

 the head when the animal is placed in its natural position. 



The most remarkable feature is the production of the cervical 

 fold into a median sjiine, as strong, and i^robably as long, as the 

 angular spines, and curved in the same fashion. 



The whole surface of the glabella, cheeks, and spines, is covered 

 with tubercles, very coarse, and elongated, on the central ridge 

 posteriorly; equally coarse, but rounded on the basal lobe; smaller 

 on the remaining portion of the glabella, and still smaller on the 

 cheeks and spines. On the largest specimens fine tubercles are 

 scattered among the coarser on the lateral and anterior parts 

 of the glabella. 



The form just described clearly belongs to the Cheiruridm, sharing 

 with them the characters — first, a trilobed glabella, the basal lobe 

 nearly circumscribed; second, the facial suture ending in the outer 



