4 TRILOBITES OF GIRVAN. 



convex, not as elevated as glabella, smooth, without median tubercle, with postero- 

 lateral angle rounded. 



Fringe narrow, nearly horizontal or slightly sloping down, not sharply marked 

 off from cheeks, composed of two concentric rows of radially arranged large pits, 

 disposed in rather widely separated radial pairs, which in middle anterior portion 

 tend to be connected, so as to form short radial grooves, in which the pores lie ; 

 towards the genal angles the concentric rows become rather wider apart, and a 

 short inner somewhat irregular row consisting of 3-4 pits is inserted at the 

 rounded postero-lateral angles of the cheeks. 



Fringe not produced genally behind posterior edge of head-shield, but ending 

 abruptly at genal angles, which bear longitudinally-grooved straight genal spines, 

 half the length of head-shield. Outer margin of fringe furnished with narrow 

 thickened border, with its outer face steeply bevelled and channelled by median 

 groove continued back along face of genal spines. 



Meso- occipital ring and pleuro-occipital segment rounded, rather prominent, 

 well marked off from glabella and cheeks by furrows. 



Dimensions. — 



Length of head-shield . . . 15"5 mm. 



■ Width of ,, ... 81-0 „ 



Length of frontal lobe of glabella . . 10'5 „ 



Width of „ „ . . 9-0 „ 



Remarks. — This species has been previously compared by me (op. cit., p. 14) with 

 T. wahlenbergi, Renault, the glabella apparently possessing similar characters. 

 There are not many points of resemblance to the true T. concenfricus, Eaton, and 

 the glabella is completely different. In T. seticornis, His., and T. bucJclandi, Barr., 

 the glabella has a lobed, not simple, neck, and the fringe is of a distinct type. In 

 T. Mbernicus, Reed,^ the tendency of the radial pits to fuse into grooves is found 

 similarly developed. 



A pygidium, probably referable to this new species, which we may call 

 T. albidus, has been found from the same horizon at Shalloch Mill, where head- 

 shields possessing the specific characters occur. It has the usual subtriangular 

 shape and obliquely bevelled striated border ; the axis is conical, about one-fourth 

 the width of the pygidium, and slightly invades the posterior border behind ; it is 

 composed of 9-10 rings, of which the first 6-7 are quite distinct, and the lateral 

 lobes show 6-7 straight radiating simple pleurae corresponding to them. Length, 



5 mm. ; width, 12 mm. 



Horizon and Localities. — Whitehouse Group (M. Bala), Whitehouse Bay ; 

 Shalloch Mill. 



1 Eeed, ' Geol. Mag.' [4], vol. ii (1895), p. 52, pi. iii, figs. 2—7. 



