106 BRITISH CAM mil AX TR1LOBITES. 



evidently allows a very large margin for inaccuracy in the original description and 

 figures. As Reed 1 has pointed out, the presence of genal spines, the more remote 

 and backward position of the eyes, the glabellar furrows, the relative shortness of 

 the glabella, the rather wide frontal limb, and the shape of the head-shield are 

 opposed to this view. To these characters may be added the course of the 

 anterior branch of the facial suture, which runs inwards from the anterior margin 

 to the eye, instead of outwards as in Cyclognathus. 



Reed himself considers the generic position of the species as still uncertain, but 

 refers it provisionally to Solenopleura. 



Horizon and Localities. — Tremadoc : Tyn-y-llan ; Penmorfa. The specimens 

 referred by Salter to this species come from the Lower Tremadoc, and the 

 specimens which he refers to Conocoryphe vexata from the passage-beds between 

 Lower and Upper Tremadoc. 



2. Beltella bucephala (Belt). Plate XIL, figs. 11—15. 



1868. Conocoryphe ? bncepliala, Belt, Geol. Mag., vol. v, p. 10, pi. ii, figs. 1 — 6. 



1873. Conocoryphe WiUiamsoni, Salter, Cat. Cainb. and Sil. Foss. Mus. Cambridge, p. 12. 



Head semicircular, with genal spines projecting backwards and outwards. 

 Glabella prominent, conical, rounded in front, separated from the anterior margin 

 by a space about equal to the width of the latter, with two pairs of somewhat faint 

 glabellar furrows, the anterior pair short, the posterior pair very oblique and 

 reaching nearly to the neck-furrow ; neck-furrow strong. Eyes small, placed 

 nearer to the anterior than to the posterior margin, distant from the glabella about 

 half the width of the latter ; ocular ridge indistinct. Facial suture apparently 

 running very obliquely outwards across the margin, then inwards and backwards 

 to the eye, and thence outwards and backwards to the posterior margin, which it 

 cuts at a distance from the glabella a little less than the width of the neck-segment. 

 Cheeks prominent, with the neck-furrow strongly marked. Free cheeks rather 

 wide. Margin broad, somewhat thickened in front of the glabella ; produced at 

 the genal angles into rather slender spines, which are directed slightly outwards, 

 and reach backwards to the sixth thoracic segment. 



Thorax probably of twelve segments, almost uniform in width up to the sixth 

 or seventh segment, tapering rapidly posteriorly. Axis in front about as wide as 

 the pleurae ; posteriorly rather narrower. Pleurae strongly bent downwards, and 

 in the earlier segments backwards, at the fulcrum, which is placed less than half- 

 way out in the first segment, more than half-way in the middle segments, and 

 about half-way in the later segments ; deeply grooved ; extremities falcate. 



Tail unknown, but must have been small. 



Dimensions. — Length when complete must have been about 30 mm. 



1 Geol. Mag. [4], vol. vii (1900), p. 253. 



