BRITISH FOSSILS. 



Head occupying more than half the entire length, and forming a 

 semicircle, exclusive of the long depending ears which reach to 

 about the middle of the tail. The glabella is pyriform, moderately 

 convex, not equal in width to the cheeks, nor reaching quite to the 

 fringed border in front, but separated from it by a narrow convex 

 space (fig. 7, h) In the strong furrow which surrounds the glabella, 

 and at the anterior part, in a line with its front edge, are placed 

 the two deep indentations characteristic of the genus * (fig. 6, a). 

 The glabella is carinate along its lower half ; it has on each side a 

 slight longitudinal depression, and at its very narrow base one 

 obscure lateral sulcus above the neck furrow. The neck lobe is pro- 

 duced into a rather strong spine, with a broad base. JNTeck furrow 

 shallow, continued along the posterior edge of the cheek, which is 

 straight half-way, and then bends suddenly down to form the margin 

 of the large triangular pendant ear ; this is slightly concave, pierced 

 by close set puncta, and bordered all round by a raised margin, even 

 at the head angles (fig 4, a), where the spines are attached. The 

 fringe which encircles the front is strongly concave on its upper sur- 

 face, with a thick flattened edge, and very convex below, except just 

 at the margin, where it is plain (see fig. 8) ; it is closely beset by 

 radiating rows of small holes, six or seven in a row. Of these rows 

 on the upper surface the two outer pores are set close together just 

 within the thickened edge, the next pore much more remote, and 

 placed at rather a greater distance from them than from the three 

 or four close set rows which range along the inner edge (see fig. 1*). 

 The fringe is equal in width all along the front, the glabella not 

 invading it, as it does in some other species. On the under side 

 (fig. 3) the fringe shows a similar arrangement, the space between 

 the second and third row being much more considerable than the 

 others, and frequently rising into a ridge. The spines are not very 

 strong ; they project abruptly from the posterior angle, and are 

 not thicker at their origin than elsewhere ; their direction is a little 

 inwards rather than directly backward. In some specimens they 

 are as long as the glabella, in others longer than it.-f* The body, of 

 six flat joints, is equal in length to the tail, and the axis alone 



* Professor M'Coy considers this an antennary pore, but this is very unlikely ; it answers 

 exactly to the place -where, from M. de Barrande's discoveries, the ascending processes of 

 the hypostome are attached. 



t The facial suture cannot be traced in this species ; in others, and especially in the 

 section Tretaspis, it runs from the upper corners of the glabella to the eye, and thence to 

 the posterior margin, just within the punctate border. I have formerly described it in 

 this position, and cannot admit the opinion that it runs round the outer margin of the 

 fringe. [See Barrande, Syst. fSil. 615, &c.] 



