TRINUCLEUS. 15 



they arc all immature individuals, as the primitive state of the fringe seems to 

 suggest a pre-adult stage. The pits of the fringe are radially arranged in two 

 concentric rows, and in front of the glabella are more or less radially fused. The 

 glabella consists of an anterior swollen ovoid portion sharply marked off behind 

 from a depressed simple cylindrical neck. No lateral furrows notch it, but at the 

 base of the swollen anterior portion two small tubercles are in one specimen 

 noticeable in the axial furrows. The surface of the glabella and cheeks is smooth. 

 With regard to affinities, the species T. wahlenbergi, Rouault, appears to have a 

 glabella with similar characters (see Rouault, ' Bull. Soc. Geol. France,' ser. ii, 

 vol. vi [1848], p. 80; Angelin, 'Pal. Scand.' [1854], p. 64, pi. xxxiv, fig. 1; 

 Linnarsson, 'Vestergotl. Oamb. Sil. Aflagr.,' 1809, p. 7<>). 



Collection.— Mrs. Gray (f. M.). 



Horizon (Hid Localities.— Whitehouse Group (M. Bala) : Shalloch Mill (f. M.) 

 and Whitehouse Bay. 



G. Trinucleus, sp. ind. (<■). Plate II, fig. 9. 



1879. Trinucleus, sp. ind. c, Nicholson and Etheridge, Mon. Silur. Foss. Grirvan, fasc. ii, p. 198, 

 pi. xiv, fig. 4. 



Specific Characters. — Pygidium broadly triangular; length 7 mm., breadth 

 18*5 mm. Axis gently convex, conical, gently tapering ; reaches posterior border; 

 consists of about 14 — 15 rings, of which only the first seven or eight are distinct. 

 Behind the first three rings the axis is faintly trilobed. Lateral lobes flattened, 

 horizontally extended, with four well-defined straight pleurae folloAved by several 

 indistinct ones. The three anterior pleurae have a narrow band on their front edge 

 and correspond with the three first axial rings. Border consisting of narrow 

 raised rim and broad bevelled portion. 



Remarks. — Certain features not mentioned by Nicholson and Etheridge render the 

 above fuller description of this well-defined and well-preserved pygidium desirable, 

 particularly as the original figure is inaccurate. It probably belongs to one of the 

 foregoing species. 



Collection.— Mrs. Gray (f. M.). 



Horizon ami Locality. — Whitehouse Group (M. Bala) : Shalloch Mill. 



7. Trinucleus, sp. ind. (d). Plate II, figs. 10, 10 a. 



Specific Characters. —Head-shield semicircular; glabella just reaching fringe but 

 not invading it, composed of large swollen ovoid anterior portion with median 

 tubercle, and of a very short well-defined neck. Cheeks convex, separated from 

 glabella by deep axial furrows. Neck-segment very narrow. Fringe narrow. 



