Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/133

Rh Head semicircular, very slightly angular in front, where it has a distinct but narrow margin. The margin is much wider on the sides, also towards the base of the free cheeks, and is there produced into rather short thick spines.

Glabella large and broad, subpentagonal, wider than the cheeks, nearly attaining the margin in front, not reaching beyond it, as in P. Hicksii, next described. It is furnished with five distinct pairs of lateral furrows, besides the neck-furrow; the two lower pairs reach directly across, the next two pairs are almost equally strong with the lower ones, but reach only about a third of the distance across; the anterior pair are short, and curve backwards at their inner extremities, and are situated somewhat in advance of the outer angles of the glabella. Eyes large, approximating the glabella at their upper part; upper edge on a line with the outer angles of the glabella, and with the fourth pair of furrows.

The glabella is unusually large in this species; and though it is angular at the apex, the angle is much more obtuse than in P. Hicksii, and is always bounded in front by the narrow margin. The neck also is much wider than that of P. Hicksii.—J. W. S.

Locality, grey beds at the base of the "Menevian Group," Porth-y-rhaw and vicinity, St. David's.

5., Salter, P1. III. figs. 1-10. Brit. Assoc. Rep. 1865, p. 285.

Apparently a very flat species; its length is from 3 to 4 inches; the breadth half the width; the general form broad-ovate, but with nearly straight sides; the short spines not interfering with the general shape.

Head sub triangular, produced in front, and terminating posteriorly in very short spines, which do not reach backwards half the length of the thorax (they are unusually short in the specimen figured in Plate III. fig. 2). Glabella very flat, and but little raised above the cheeks; it is unusually long, reaching even to some distance in advance of the front margin, pear-shaped, attaining its greatest width about the anterior third, where it is wider than the cheeks. Thence it tapers forwards to the obtusely pointed front, and backwards, with straight sides, to the narrow neck segment, which is only one-fourth the width of the head.

Four distinct short furrows indent each side of the glabella, equally strong with the neck-furrow; and the lobes thus marked out are of equal size. Some specimens show traces of a fifth pair anterior to these, which bend back at their extremities towards the next pair. These, however, are generally very indistinct. None of the glabella-furrows extend quite across, but leave a somewhat elevated space down the middle of the glabella; nor do they quite reach the axial furrows, which are well marked.

The eyes are about halfway up the head, and occupy about half the length of the cheeks; they are gently curved downwards and