32 SILURIAN TRILOBITES. 



Phacops (Acaste) Jamesii, Portlock. PI. 1, figs. 39 — 41. 



Phacops Jamesij, Portlock. Geol. Report of Tyrone and Londond., p. 283, pi. 3, fig. 10, 

 1843. 



— — Salter. Decades Geol. Survey, No. 7, art. 1, p. 10, 1853. 



— — — In Morris's Catalogue, 2nd ed., p. 113, 1854, &c. 



P. {Acaste) unciam latus ; capite semicircular \ fronte subangulato marginato 

 crasso. Glabella fere plana tuber culata, antice latissima, postice ad dimidium contracta, 

 lateribus rectis : lobo frontali late trigono, oculos impendente ; cater is radiant ibus, supremo 

 maximo trigono, medio lineari obliquo haud abbreviafo, basali transverso ; lobis omnibus fere 

 ad medium glabella, spatio angusto interjecto, conniventibus. Gena declivce marginatcB, 

 angulis obtusis. Oculi abbreviati valde curvi. Thorax ? Cauda rotundata, quam longd 

 tertiam partem latior, depressa ; axi satis magno conico, marginem nullo modo attingente, 

 annulis 8 — 9 ; lateribus sulcatis, sulcis 6 — 7 aqualibus, Iceviter per totum interline atis. 



I have seen but four or five specimens of this. But the species is not uncommon in 

 Waterford. It is a marked one, conspicuous for the flatness of the glabella, and the 

 thickened outer border. The cheeks are triangular ; the eyes have a peculiar angular 

 upper lobe. The tail is a good deal like that of Calymene, and the whole aspect is unusual 

 for Phacops. Portlock's figure, which, like all the rest of his plates, were but second- 

 hand office copies of Mr. Dunoyer's beautiful drawings, 1 gives no proper idea of the 

 species, which is named in honour of Lieut. -col. James, of the Ordnance Survey. 



P. Jamesii must have been nearly two inches long. It is very gently convex, the head 

 flattened above, the cheeks declining rather steeply. The glabella, covered closely with 

 not very coarse tubercles, occupies much more than half the width of the head, especially 

 in front, where it is very broad, the sides converging behind at about 70°. The forehead- 

 lobe is abruptly wider than the rest, overhanging the eye. It is transverse, subangular 

 in front, with a thickened margin, and behind bounded by the nearly straight upper 

 furrows, which run far towards the middle, and are of equal strength throughout. The 

 other furrows radiate, the middle ones declining towards the base of the eye. The 

 basal ones more direct, nearly parallel to the neck-furrow. The axal furrows are very 

 faint. 



The eye is small, strongly curved, set near the glabella, and on a level with it ; the 

 upper eye-lobe is pointed, the lentiferous surface imbedded, as it were, in a fold of the 

 cheek, which is here convex, but declines all round, and slopes away to the margin. The 

 cheek itself is triangular, with obtuse outer angles, and is only granular, not tubercular, 

 strongly marginate on the outer side, and with a sharp neck-furrow, which does not meet 

 the marginal furrow. 



Tail semicircular, one third wider than broad, depressed (this is not due to pressure). 



1 The original plates were found to be rather too large, and unfortunately had to be cancelled. 



