648 THE LOWER SILURIAN PERIOD. 



middle part is produced into a very short conical tubercle-like spine, 

 directed sliglitly backwards. The cheek-lobes are strongly gibbous, and 

 very regularly arched, the convexity being stronger anteriorly. A nar- 

 row distinct wavy ocular ridge begins on the cheek-lobe, just opposite the 

 anterior part of glabella, and, thinning gradually out and arching, at 

 first slightly forwards, curves round and is directed towards the outer 

 angle of cheek-lobe, but it usually vanishes before reaching that point. 

 From its anterior outer side it throws off a very numerous set of fine 

 bifurcating raised lines or ridges. These lines are directed outward 

 from the primary line at a rather acute angle, and appear to bifurcate 

 several times. This ocular ridge is thickened at its commencement, 

 but is not so strongly marked at that point as in C. Baileyi, It is 

 also more arched forward than in the latter species. The whole outer 

 surface of shield is covered by innumerable, close-set, raised points or 

 granulations just visible to the naked eye, but very distinct under 

 the lens, appearing in the impression of the shield as minute punctures. 

 These appear to be more distinct on the convex portions of the shield. 

 The raised margins, cheek-lobes, glabella, occipital ring, as well as the 

 lobe just in advance of the glabella, bear sparsely sown, minute, short 

 spines, Avhich give to the surface a distinct granular appearance. 

 These are always wanting in the furrows and on the cheek-lobes, 

 are more crowded on the outer halves of the cheek-lobes. They are 

 true spines, but usually appear as granulations on the casts. 



In very young specimens, a line in diameter, the shield is semi-circular, 

 the cheek-lobes are extremely gibbous, and very much more convex 

 than the glabella, and the pre-glabellar lobe is very conspicuous. 



I take great pleasure in dedicating this the most abundant and 

 prettiest of these Trilobites to its discoverer and my intimate friend 

 and geological companion, Mr G. F. Matthew. Common at Rat- 

 cliffe's and St John's. Specimens from Coldbrook show slight differ- 

 ences, probably only varietal. 



Conocephalites Robhii, Hartt, MS. Head without movable cheeks, 

 of moderate size, depressed convex, slightly arched in front, where the 

 width is considerably less than behind. Length about equal to breadth 

 in front. 



Glabella, ovate-conical, sides straight, and dorsal furrows so inclined 

 as to meet if produced in middle part of anterior margin ; very convex ; 

 more elevated in the middle ; posterior furrows reaching about one- 

 third of the way across the glabella, directed strongly backwards, and 

 reaching nearly to the base of glabella ; middle furrows less distinctly 

 marked, short, not so oblique as first ; antei'ior very short, appearing 

 only as little pits or depressions on the sides of the glabella. 



