142 SILURIAN TRILOBITES. 



young specimen, has only four rings, and this is the true number in this specimen, and is 

 not due to accident. The ribs of the tail are more conspicuous in proportion than in 

 the somewhat older specimen, fig. 2, which has truly seven rings ; while in fig. 3 the 

 eighth thorax-segment is becoming visible (see fig. 3 a). 



Locality. — Llandeilo Flags. Two or three places near Builth, Radnorshire, viz. : 

 Wellfield; (figs. 1, 3), and Pencerrig, (Mus. P. Geology fig. 2) ; also Gwernyfyd (Mr. J. 

 E. Lee's cabinet, fig. 4). 



Subgenus — Barrandia, M'Coy, 1849. 

 Barrandia (Barrandia) Cordai, MCoy, PI. XIX, fig. 5. 



Barrandia Cordai, M'Coy. Annals Nat. Hist., 2nd ser., vol. iv, p. 409, 1849. 



— — Id. Synopsis Pal. Foss. Woodw. Mus., p. 149, pi. iv, fig. 1, 



1851. 

 Ogygia Portlockii, Salter. In Morris' Catalogue, 2nd ed., p. 1 12. 1854. 



B. uncialis, ovata, vel caput, thoracem, caudam aqualis. Oculi post medium capitis 

 positi. Pleura retrocurvce, hrevisulcatce. Cauda axe inteyro, laterihus unisulcatis. 



One specimen only of this most distinct and characteristic species is known, and it is 

 a perfect one in the Woodwardian Museum. But I believe it is a common fossil, and 

 it should be sought for at Builth. I had no excuse for uniting this very distinct form with 

 the B. Portlocki. 



Length 11 lines (our figure is enlarged to once and a half the natural size), of which the 

 head, thorax, and tail are nearly equal parts. The semi-oval head is rather more than twice as 

 wide as long, lunate, with a concave hinder border and obsolete neck-furrow. The axal- 

 furrows are parallel below, slightly converging at less than half-way up the head, and then 

 obsolete. The front margin concave, the border of the cheeks extremely narrow ; the large 

 slightly curved eyes placed much nearer the axis than the border, and very near the hinder 

 edge. 



The facial suture curves slightly out above the eye ; and beneath it cuts the posterior 

 margin below the eye, and very remote from the short spinous angles. 



Thorax with its slightly convex axis very little less in width than the pleurae, and 

 tapering backwards ; the rings a good deal arched forward, and strongly grooved across. 

 The pleurae are oblique backwards, and falcate at their tips ; with a short, strong, obhque 

 groove not half their length, and the fulcral point very prominent (as in some of the 

 OlenidcB, for instance, Bemopleurides). 



The tail is half as wide again as long, and the front much arched to follow the form 

 of the retreating pleural segments. The axis short-conical, extending less than two thirds 

 down the tail, pointed, not prominent at the tip, and without furrows. It is well 

 distinguished from the gently sloping sides, and the border is very gently concave. One 



