Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/131

Rh fulcrum, which is placed rather far from the axis; the spines comprise rather more than a third of the whole length of the pleuræ, and are rather dilated at the base. Our figure does not show these spines; but better specimens have lately been discovered. Tail unknown. This species is easily distinguished from any of the others found in the "Menevian Group" by its large size, wide anterior margin, the small, highly convex, and deeply furrowed glabella, and wide cheeks. Its nearest ally is a new species (C. perdita, P1. II. fig. 3), found by me at the end of last summer, about 200 feet lower down in the Cambrian series (purple and grey beds); but as the last-named species is smaller, and has a far less strongly developed anterior margin, as well as a wider glabella, it is not likely to be mistaken for it, especially when we recollect that the one occurs in the purple Cambrian beds and the other in the "Menevian Group," and that as a rule the range of the species in these lower series extends through but a slight thickness of the strata.—H. H.

Locality—Grey beds at the base of the "Menevian Group." Porth-y-rhaw, St. David's.

Length from ½ to 1 inch, breadth about ½ inch. Form broad-ovate, depressed. Head semicircular, rather wider than the body, surface very slightly tubercular, marginate all round, and angles produced into short strong spines. Glabella parabolic, more or less convex, and indented by three lateral furrows, which, however, are rather indistinct in the most convex specimens; the cheeks are broad and compressed, and bear small but prominent eyes rather remote from the glabella, being distant from it by a space about equal to its width, and connected with it by strongly marked ocular ridges; the facial sutures run forwards and rather outwards above the eyes, and backwards and outwards below, cutting across the hinder margin near the outer angles. Thorax of 14 rings, axis slightly convex, and tapering towards the tail; pleurae long and narrow, twice as long as the rings of the axis, deeply sulcate, and bent slightly backwards at the fulcrum, which is placed about midway. Tail semicircular, with a tapering, pretty strongly marked axis of three segments; limb marked by three ribs, marginate. This species is distinguishable from C. variolaris by many of the characters above given, but especially by the want of the very strong tuberculation and the strongly raised margin of the latter species—and also by the presence of a well-defined ocular ridge, which, if present, is scarcely at all visible in C. variolaris. C. applanata has no tubercle on either the axial rings or pleurae, and is altogether a much smaller species than C. variolaris.—H. H.

We have been fortunate in finding the very young of this species; it is a capital example of the metamorphosis observed by Barrande in so many of his Primordial forms. The little disk, not more than half a line long (fig. 6 b), shows, when magnified (fig. 6 a), no trace of