﻿Vol. 66.~] THE CAMBRIAN ROCKS OE COMLET. 41 



is limited posteriorly by the steep fall of the surface to the 

 posterolateral limb, and anteriorly the surface falls gradually, in 

 advance of the ocular ridge, into the hollow part of the frontal 

 limb. 



Eye-lobe. — One-third of the length of the head ; the posterior 

 •end reaching to the postero-lateral limb ; the anterior end marked 

 by a rather sudden falling-away in altitude where it joins the 

 ■ocular ridge ; distinctly elevated throughout above the hollow in its 

 rear, but not so high as the fixed cheek. 



Ocular ridge. — A ridge, rounded rather than flat; arising 

 i'rom the axial furrow nearly as far forward as the little impressions 

 representing the anterior pair of glabellar furrows ; passing across 

 the cheek in a bold curve to the eye-lobe, and having a slight 

 hollow (not an impressed line or furrow) behind it. 



Postero-lateral limb. — Marked by a wide groove passing 

 directly outwards, and a convex marginal rim, which is strongly 

 geniculate at a distance out nearly equal »to the width of the 

 glabella ; beyond the geniculation the surface of the limb falls 

 steeply down to the facial suture. 



Frontal limb. — About a fifth of the total length of the head- 

 shield ; consisting of a deep hollow and an equally wide and very 

 ■convex rostral margin. These features lose intensity to right and 

 left, and at the same time the limb curves downwards considerably. 



Facial suture. — Hardly visible from above, owing to the 

 -curving over of the sides of the cranidium ; anterior branch short 

 and subparallel to the axial line ; posterior branch a short curve, 

 .convex outwards ; both branches less far out than the eye-lobe. 



Test. — Probably rather thick and firm, but usually found 

 weathered to a snowy-white powdery substance. The external 

 •cast [188] (PI. VI, fig. 2) shows that it was covered nearly all over 

 with closely set pustules or pustular spinelets (I have been unable 

 to make a clear wax impression of these, but the holes in the cast 

 appear to be pointed). These pustules have no corresponding 

 impressions on the interior, and the internal cast [186] is conse- 

 quently quite smooth (PI. VI, fig. 1). The marginal modification 

 is unknown. 



Thorax. — Associated with these cranidia are a number of frag- 

 ments of thoracic segments, some of which exhibit very similar 

 -surface-characters. One of these, an axis ring [196], is represented 

 in PI. VI, fig. 3, and is, with reserve, referred to the species 

 under description. The crust is partly weathered away, but 

 enough is left to show the bases of the pustules which covered the 

 convex body of the axis ; the front articulating portion is quite 

 smooth, and in the groove the pustules are smaller. 



A beautiful little upright spine stands on the centre of the ring ; 

 when found it was complete, now the point is unfortunately gone : 

 it was quite smooth. 



The pleurae have not been sufficiently studied for description. 



Localitj 7 and horizon. — Oomley, from the French grey and 

 lower part of the grey limestones of the excavation, 200 yards 



