Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/132

54 eyes or facial suture. Only two, instead of fourteen, body-rings are visible; and these, as well as the head, are crowded with those characteristic tubercles which are so common in embryo forms of this group, and which indeed are retained long after in certain species and genera. The tail is of the ordinary type, a good deal developed for the size of the animal, and marked with two or three distinct segments, tubercular like the rest.

In these young forms it is impossible not to see the representatives of genera such as Agnostus, which has two, and Microdiscus, which has four rings in the adult state. The cylindrical unfurrowed glabella and the want of eyes, the few body-rings and the great relative development of the tail, are as conspicuous in the embryo of Conocoryphe as in the adult state of the humble forms above quoted. What is the precise nature of the tubercles which are so conspicuous in the embryo of Sao, for instance, as given by Barrande, it is difficult to say. I have called attention to them elsewhere.—Mon. Pal. Soc. Trilobites. Monograph, pt. 1 (under Phacops), pl. 3, p. 52.—J. W. S. Locality—"Menevian Group," Porth-y-rhaw, St. David's; also near Maentwrog and Dolgelly, North Wales.

Of this curious species, a part of the head and six thoracic rings only have been found. These, however, show characters sufficiently marked to indicate that it is specifically (if not generically) distinct from either of the others.

The glabella is large and elongated, reaching apparently to the frontal margin, not furrowed, but sharply ridged centrally, separated from the cheeks by very deep dorsal furrows. Cheeks narrow, convex, and acutely triangular, surface smooth, with no trace of ocular ridges, or facial sutures, or of being strongly marginate; a very strong spine occurs on the neck segment.

The thoracic axis is highly convex, and spinous along the centre; the pleurae are wide, very deeply furrowed, and terminate in long, tapering spines, which curve sharply backwards; the fulcrum of the pleurae occurs about midway from the base of the spines to the axis. The pleurae, without the spines, are only a little longer than the width of the axis, and bend sharply at the fulcrum.

Locality.—"Menevian Group" (middle beds) Porth-y-rhaw, St. David's.

A few rather imperfect heads, some loose free cheeks, and unattached pleurae only have as yet been found; but these are sufficient to indicate a new and very distinct species. Its position, also, in the grey rocks, at the very base of the "Menevian group" renders it a most important species, and necessitates its description even in this imperfect state.