2 



BRITISH FOSSILS. 



part, occupies two fifths of the entire length ; it is regularly and 

 highly convex. The glabella is encircled by a distinct furrow ; it is 

 smooth, almost gibbous, broadest in the middle, and forming a com- 

 plete oval, if the neck segment be included : there are no traces of 

 glabella lobes, but the neck furrow is strongly marked. 



The cheeks are not half the width of the glabella, steeply bent 

 downwards, and seen without the free cheeks, much narrower for- 

 wards than towards the blunt squarish posterior angle. They are 

 confluent in front with a narrow anterior margin. Their poste- 

 rior side is traversed by the continuation of a deep neck furrow. 

 This furrow runs near the edge at first, but soon diverges, and 

 towards its end turns abruptly upwards to the outer margin of the, 

 cheek (fig. 6, a). The posterior margin, thus separated, is rendered 

 conspicuous by being, like the glabella, quite smooth, while the rest 

 of the cheek is covered by a lineation parallel to the edge, which 

 also continues round the front. 



The facial suture (see figs. 6 and 7) is marginal for a less distance 

 than the width of the glabella in front, then turning downwards in 

 a gentle curve, it crosses the cheek very obliquely, and ends on the 

 outer margin at the point where the neck furrow turns up to meet 

 it. There is a slight indentation in it opposite the front end of the 

 glabella, indicating the place of the very forward eyes, but its 

 general course is but very little bent or sigmoid. The free cheeks 

 are absent in all our specimens, but from the shape of the rest of the 

 head, and analogy with similar forms of trilobites, they must have 

 been quite linear, rather broadest in front to complete the half- 

 elliptic form of the head, and attenuated behind. We have restored 

 them, h, and indicated the probable position of the small eyes at 

 c, in fig. 6. 



The thorax is nearly parallel-sided, often partially coiled up, of 

 seven* convex rings, the axis of which is prominent and as broad as 

 the sides, in front rather broader. The sides of the axis in each 

 segment are not sharply defined by a longitudinal furrow, but run 

 out a little into the groove of the pleurge, as in fig. 6, d. These latter 

 are truncate and square at the ends, facetted anteriorly for rolling 

 up, and, have the pleural groove very deep, and reaching nearly to 

 the tip, where it ends abruptly; it divides the pleura unequally, — 

 the anterior portion is the largest. The fulcrum is placed at less 

 than half distance from the axis, and from a little beyond this point 



* At least in the only specimen (not a full-grown one) -which has still the parts in situ. 

 One specimen has the appearance of possessing another ring, but it is indistinct. 



