52 PROCEEDINGS OF THE GEOLOGICAL SOCIETY.
in a series of red and purple rocks several hundred feet lower; and
these will be described by-and-by*. The present communication
illustrates only some characteristic Trilobites from the grey beds at the
base of the "Menevian Group," and two forms from the black slate
series directly above these beds.
Of these we only describe at present Paradoxides and Conocoryphe, and complete these genera so far as they are yet known in the "Menevian Group" proper. The several species in the genera Erinnys or Harpes, Arionellus, and Agnostus, are still to be described.
1. Conocoryphe BUFO, Hicks, P1. II. fig. 8. Brit. Assoc. Report, 1865, p. 285.
Of this well-defined species, only a few separate heads, and one with six body-rings attached, have been found. It is much the largest species of the genus yet found in the "Menevian Group," being probably no less than 3 inches in length and 1-1/2 in breadth across the head. The head is semicircular, tubercular all over, strongly marginate, with the angles produced into short spines. The glabella occupies nearly two-thirds the length of the head, is very narrow forwards, parabolic and convex, and is indented by three distinct lateral furrows on each side, which run obliquely backwards and reach about one-third of the distance across; length about equal to width at the base, centre ridged slightly, neck-furrow deep, well defined, and arched somewhat upwards in the centre. Occipital ring almost as convex as the hinder part of the glabella. Cheeks wider than glabella, almost equally convex with it, and separated from it by very deep dorsal furrows; their posterior margin is narrow, bent forward near the outer angles, and bears a strong tubercle on either side. Eyes small and scarcely visible, placed very far from the glabella. The facial sutures curve outwards above the eyes, and beneath them are nearly marginal, just cutting off the spinous angles. The outer border, which is narrow round the cheeks, becomes greatly exaggerated in front, and widens to a triangular tumid boss, the apex of which reaches backwards almost to meet the anterior part of the glabella; in consequence of this the marginal and dorsal furrows approximate each other, and become almost merged into one another at this spot. This boss is at least a fourth of an inch wide opposite the apex of the glabella, rises suddenly upwards from the marginal furrow, and then slopes forwards gradually. The whole surface is granular, with some larger tubercles. The thorax, of which six rings only have been found attached, has a highly convex axis, about half as wide as the pleurae with the attached spines; pleurae depressed, grooved widely in the cast† and turned sharply backwards at the
- It is perhaps advisable to mention what these are, leaving their description
till another time:—A new genus, Plutonia, a Conocoryphe, a Paradoxides, a Microdiscus, Agnostus, Theca, Lingulella, and a new bivalved Crustacean. It really does look as if the changes rung on these early forms were not so much varied as we descend lower in the geological scale. Hence we may hope to reach some point beyond which the variations are zero.—J. W. S., Dec. 1868.
† The shell is probably very thick, and the groove on the upper crust would not be nearly so strong as in the cast.
