66 BRITISH CAMBRIAN TRILOBITES. 



2. Parabolinella csesa, sp. nov. Plate VII, fig. 2. 



Glabella almost rectangular, narrowing slightly forwards, with the anterior 

 angles rounded, separated from the marginal farrow by a space rather less than 

 one-fourth the length of the glabella ; three pairs of glabellar furrows, none of 

 which reach either the middle line or the axial groove; the first pair short, nearly 

 at right angles to the axis ; the second pair longer and more oblique ; the third 

 pair sigmoid, giving off towards the side a small posterior branch ; neck-furrow 

 shallow towards the middle, ueck-segment with very indistinct traces of a median 

 tubercle. Eyes placed about halfway between the anterior and posterior margins, 

 very near to the glabella ; ocular ridge short and slightly oblique. Facial suture 

 running backwards and inwards to the eye and thence backwards and outwards. 

 Margin formed by a narrow raised rim. 



Thorax of sixteen segments. Axis as wide as the pleura? in the front part of 

 the thorax, but in the hinder part not much more than half their width; no median 

 tubercles visible. Pleura? nearly straight and horizontal, bent very slightly down- 

 wards and backwards at the fulcrum, which in the anterior pleura? is about halfway 

 out, in the later segments becomes gradually farther out and less distinct; pleural 

 grooves oblique, the anterior pleura? facetted and terminating in short points 

 directed outwards, the later pleura? not facetted and ending in short falcate points 

 which curve backwards. 



Tail fairly large, semicircular, marginate. Axis forming less than one-fourth 

 the total width, ending bluntly some distance from the margin, but connected with 

 the margin by a faint ridge; three distinct rings besides the terminal portion. 

 Lateral lobes wide, with three furrows, interlined. Margin narrow. 



Dimensions. — About 20 mm. long. 



A comparison of this description with that of Parabolinella williamsoni will 

 show at once that the two forms are very closely allied, and it is with some hesita- 

 tion that I separate them, for the differences may be due in part to the mode of 

 preservation. The specimen here described has been compressed from front to 

 back; the specimen of P. williamsoni has hardly been compressed at all and only 

 slightly distorted. P. williamsoni, however, has only two pairs of glabellar 

 furrows with no trace of a third, Avhile in P. csexa the three pairs are quite 

 distinct, and the last pair shows the branching which is seen in several other 

 species of Parabolinella but not in P. williamsoni. In their general form the tails 

 of the two species are similar, but in P. williamsoni the axis ends in a cone which 

 reaches the margin, in /'. csesa it ends bluntly, and the rounded termination is 

 connected with the posterior margin by a slightly raised narrow ridge. The 

 margin appears to be narrower in P. cxsa, but this is probably because it is less 

 perfectly preserved. 



Horizon ami Localiti/. — Upper Lingula Flags: Dolgelly. 



