Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/134

56 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. outwards, following nearly the outline of the cheeks. Their upper end is very close to the glabella at its widest part.

The cheeks are triangular, the margin smooth; the surface within it is scrobiculate, but not deeply so. Their margin, which is wide at the base of the spines and sides, is almost entirely lost in front by the overlapping of the large glabella. This is only the case in fully grown specimens (fig. 2.); in the young (figs. 8, 9, & 10) the margin is equal all round, and a considerable space, also, separates the glabella from the anterior margin. This space gradually diminishes as the individual grows; and the glabella enlarges until, as in the fully grown specimen (fig. 2), the margin becomes completely obliterated.

The labrum (fig. l a) is curved, expanded at the base, and truncate at the end, with the angles rounded.

The thorax consists of nineteen rings; axis convex, tapering, and rather narrow, being about a third less than the width of the pleurae (including spines) anteriorly, whilst posteriorly, for the last six or seven segments, it is scarcely half as wide, the pleurae having increased in length, whilst the axis has been gradually tapering. The pleurae are compressed and deeply grooved obliquely to a little beyond the base of the spines; the upper fourteen terminate in short spines, which turn abruptly backwards, and at about the same angle. In the hindmost pleurae the spines are somewhat lengthened, but are still very short indeed for this genus, and are exactly like the two front pleurae of the tail. The latter is composed of two nearly free segments, with short spinous pleurae (fig. 5), and an appendix, which is almost circular and has one pair of lateral ribs only. It has a broad axis, marked by five annulations, the hinder one being much elongated, and indented slightly along the middle of its length. The limb of the broad circular appendix (fig. 6) is quite distinguished from the two front pleurae, and is depressed, and marked by two furrows, which terminate in the wide margin. The upper pleurae are grooved nearly to their tips. Margin of limb strongly marked, and somewhat raised.—H. Hicks.

The close observer can hardly fail to be struck with the sort of intermediate character borne by this species. It reminds us almost equally of Paradoxides and Anopolenus. The shortened spines to the body and tail, the long, narrow, and strongly margined eye, the transverse, equal, parallel side-lobes of the glabella, the distinct anterior margin to the head (on the young specimens at least), the squarish, not wide, truncated labrum, and the compound tail, all tend to connect this old species, first with such further-developed forms as Anopolenus(?) or Paradoxides Loveni, Angelin, of Sweden, and, through them, with Anopolenus itself.

In speaking of the compound tail, I would not be too confident that the two pleurae really form part of it. But we cannot deny that several of the species really have a pair of long-spined pleurae attached to the upper border of the tail itself, though their connexion with the rounded or squarish appendix is not evident in general. In