BRITISH FOSSIES. 3 



spine, which is much shorter than the width of the cheek. The eye 

 is placed midway up the head, a little in advance of the greatest 

 convexity of the cheek, and at one third outwards from the glabella, 

 with which it is connected by a very slightly prominent ocular ridge 

 (perhaps stronger when the crust is perfect). The facial suture ap- 

 pears to run along with this ridge forward, and behind the eye it 

 takes an outward direction and cuts the posterior margin just under 

 the base of the angle spine. The neck furrow is very strong, and is 

 overhung by the gibbous inner base of the cheek. 



Glabella broadly triangular, not very convex, with a distinct 

 median lobe and two pairs of round lateral lobes, besides a third 

 upper pair, which are small and not distinctly separated from the 

 cheeks. The basal lateral lobes of the cheeks are equal to the median 

 lobe' in width, and are well separated from the most convex portion 

 of the cheeks ; above they are fused with them, as is also the upper 

 or second lobe on its outer edge, but both of these lobes are circum- 

 scribed above and below, and on their inner edges by deep furrows ; 

 the glabella appears on the whole to^ be quite distinct from the 

 cheek. The neck segment is not cut off by any distinct furrow ; it 

 is convex, expanded backwards, and produced into two somewhat 

 divergent spines, about equal in length to the glabella. The front 

 of the head is truncate, and its middle portion as usual free from 

 spines. Surface of the head covered with large and small granules, 

 set thickest on the glabella and gibbous base of the cheeks. 



Thorax horizontal, except the very convex axis which occupies 

 rather more than a quarter its width ; of 9 segments, which are 

 each semi-cylindrical (plevre d hour relet, Barrande), and ornamented 

 with granules (fig. 2). They terminate in a strong spine equal in 

 length to the pleura, and bent backwards at right angles to it on 

 the hinder segments ; in the forward ones the spines are shorter, 

 and set at an obtuse angle. When the interior cast of the thorax 

 Ib examined (fig. 3), the pleurae are not seen as semi-cylindrical, but 

 much flatter, and a broad raised ridge runs obliquely along their 

 upper border, leaving a flat space behind. This is, of course, due to 

 the different thickness of the crust at different points. 



Tail minute, semicircular, with a small, narrow, and convex axis 

 of two joints,, the limb flat, except the convex ridge which runs ob- 

 liquely from the axis to the primary spine on each side.. These 

 spines are directed backwards, parallel to each other, and extend 

 nearly as far as those which run out from the last of the body 

 segments. Between these are six small equal marginal spines, and a 

 pair of similar spines outside the large ones on each side of the tail. 



