2 



BRITISH FOSSILS. 



Description. — The general form is depressed and elliptical, the 

 length about 1 J inch, the breadth 1 inch. The contour of the head, 

 which is exactly as long as the caudal shield, and more than one- 

 third the whole length, is nearly a true semi-oval, evenly convex 

 except on the median line behind (which is abruptly raised), and 

 slopes on all sides to a concave border. The glabella, scarcely defined 

 at all in front, though faintly indicated (more strongly so in young 

 specimens), is of a pyriform shape. Posteriorly it is much con- 

 tracted, and again suddenly expanded upon the neck border. Its 

 greatest width beliind is not above one-fifth that of the head. The 

 eyes are small, convex, much curved, placed at less than their own 

 length from the hinder margin, opposite the contracted part of the 

 glabella, and rather further apart than the width of the thoracic 

 axis. The facial suture runs out nearh^ at right angles beneath the 

 eye, and in front of it describes a large arc, diverging fiom the eyes 

 at an angle of 70°, and cutting the anterior border far outwards, in 

 a line overhanging the fulcral points. The facial suture is strictly 

 marginal in front, and the hypostome, fig. 4, appears to be quite con- 

 tinuous, without a rostral shield as in Illcenus, or a vertical suture, 

 as in some AsapM. 



Two good specimens in Dr. Wyville Thomson's cabinet show the 

 labrum, but its margin is broken off. It is wide at its attachment, 

 considerably convex in the middle, more so than in Asaphus, and is 

 marked with concentric lines on the sides. There is not enough to 

 show that there was no marginal groove, or whether the tip was 

 rounded and entire, as in Illcenus, which is most probable. 



Thorax of nine rings, not so long as the head, and with its axis 

 only two-thirds as wide as the pleurae, convex. Pleurae flat as far as 

 the fulcrum, which is about the width of the axis remote from it. 

 Thence the pleurae are bent down and a little back, and facetted 

 for rolling up. There is no groove whatever to the pleurae, which 

 thus resemble those of Illcenus. 



Tail semi-oval, blunt, not convex, the conical axis about half the 

 width of the sides, and reaching fully two-thirds the length of the 

 tail. Our figure 2 g. has it too long. The axis has about eight faint 

 furrows. The sides are gently convex at first, and then broadly 

 concave, with a somewhat sharply defined margin ; it is without 

 any furrows, — even the usual upper one is obsolete, or nearly so. 

 The apex is very blunt, more so than the front of the head. The 

 incurved striated portion is broad, and not indented by the point 

 of the axis. 



