646 THE LOWER SILURIAN PERIOD. 



deep and wide. Sides of shield bent slightly downwards. Posterior 

 angles flattened. Cheeks sub-triangular, bounded by the straight 

 dorsal furrow, the straight groove which separates them from the 

 glabella, and the curved marginal furrow. They are more convex 

 or gibbous than the glabella, sloping gently towards the marginal 

 furrow, but steeply to the other bounding grooves. In the cast 

 they are marked on the edge of the bounding groove of the glabella 

 at the points where the straight sides of the latter begin to curve 

 around the front by two small, low, but well-marked ocular pro- 

 minences, from each of which extends a slight ocular ridge, with a 

 more or less outward curve towards the posterior angle of the shield, 

 but usually losing itself at about half the distance in a system of 

 delicate ramifications, which may often be traced to the posterior 

 angles of the cheek lobes. Like ramifications are thrown off for the 

 whole length of the ridge from its anterior side, and these occupy the 

 surface of the cheek-lobes in front of the line. The surface of the 

 cast sometimes appears granular, but the mould is always smooth, 

 and the outer surface of the shield was unfurnished with tubercular 

 or granular ornamentation. The posterior border on each side of 

 glabella is very elevated in the middle, and loses height thence 

 each way. Cephalic shield sometimes an inch and a half in width. 



Heads only of this species have been found. They occur in 

 moderate abundance in the primordial shales of the St John group 

 at Ratcliflfe's Millstream. Collectors, Professor L. W. Bailey, G. F. 

 Matthew, J, W. Hartt, and C. Fred. Hartt. 



Fig. 224. — Conocephalites MattJiewi, head.* 



Conocephalites Matthewi, Hartt, MS. (Fig. 224). Head, semi- 

 circular to semi-elliptical, more than twice as wide as long; front 

 and lateral margins forming a regular curve ; posterior margin 

 nearly straight ; posterior angles of shield flattened and rounded 

 without spines ; mai'gin with a strong, round, rather narrow fold, 

 which becomes narrower and lower towards the posterior angle of 

 shield, where it disappears. This is separated from the cheek-lobes by 

 a very deep, moderately broad groove. This groove is arched forward 

 in front by a large semi-globose swelling, situated just in advance of 



* Owing to the difficulty of drawing from imperfect and distorted specimens, this 

 and the following figures do not adequately represent all the characters of the species 

 as described by Mr Hartt. 



