2 



BRITISH FOSSILS. 



There is less difficulty about the name of the sub-genus. That 

 bestowed by McCoy is convenient enough, the group being a really 

 good one, distinguished by the soldered head sutures and especially 

 the absence of eyes.* No trace can be seen of these organs in the 

 present species. 



Description. — Rarely exceeding an inch and a quarter long, of a 

 broad oblong-oval shape, the head being nearly one-third the whole 

 length, convex, and divided deeply into three tumid lobes, of which 

 the lateral ones or cheeks are not above half the width of the 

 glabella. This is " sub-rhomboidal,'' or spherical-triangular, convex, 

 smooth, twice as broad in front as behind, where a very narrow pair 

 of basal lobes separates it from the neck-ridge ; the upper furrows 

 are quite obsolete. The cheeks are trigonal, the shortest side being 

 the outer or marginal side, very evenly convex, and with no trace 

 of an eye. They are bordered by a very distinct and rather broad 

 smooth margin, which is continuous at the rounded posterior 

 angles of the head, and lost in front, where it abuts against the 

 glabella. 



Thorax of 11 segments, with convex narrow axis and rounded 

 pleur£e ; the segments of the axis tuberculate at the sides ; the 

 pleurae not much bent back, rounded at the end, the groove narrow 

 and short, the fulcrum placed at less than half way out ; the facet 

 rather large. 



The tail is short and broad ; its length not half its breadth, 

 and both forward and hinder edges being curved, so as to give a 

 lenticular outline. The axis is suddenly narrower than that of the 

 thorax, conical and gently convex, attaining very nearly the border 

 of the tail, blunt at the tip and marked with four or five transverse 

 furrows. The sides have four radiating bent furrows, which are 

 faintly interlined and nearly reach the edge ; there is no distinct 

 border to the tail. 



The species was first figured in England (from the only English 

 locality I know of, viz., the Knowl Hill, near Newton Bushell,) in 

 the plates executed by Sowerby for the Devonshire Memoir of 

 Professor Sedgwick and Sir R. I. Murchison.f That figure is from 



* Trimerocephalus has been lately made to include all the species with lobeless or very 

 faintly lobed glabella and soldered sutures and superficial minute eyes, e.g., Phacops 

 Volborthi, Barrande, and P. cryptophthalmus, Emmrich, which last is figured on our plate 

 for comparison. But it will probably be hereafter restricted to the present species and 

 kindred forms, since the most carefiil scrutiny fails to detect the least trace of eye or 

 facial suture. 



f Trans, Geo], Soc, 2nd series, vol. v., 1840. 



