26 TRILOBITES OF GIRVAN. 



Famibj Bronteid.*. 



Genns BRONTEOPSIS, Wyville Thomson. 

 Bronteopsis scotica, Salter. Plate IV, fig. 6. 



1904. Bronteopsis scotica, Salter, Eeed, op. cit., pt. ii, p. 94, pi. xiii, figs. 5^13. 



In the previous description of this species the characters of tlie free cheeks 

 could not be quite fully given owing to the poor material available. But we are 

 now in a position to remedy this. 



The free cheeks are found to be triangular and transversely elongated in shape, 

 about twice as broad as long, and are produced backwards into a tapering genal 

 angle acutely pointed at about 30°. The inner portion of the cheek is swollen, 

 rising up steeply to the eye and forming a quarter of a circle in shape with a 

 radius equal to about half the length of the whole free cheek. The outer marginal 

 portion is depressed, sloping down to a rather broad slightly concave border not 

 marked off by any distinct furrow, but only separated by a shallow depression 

 which is most clearly developed towards the genal angle. The surface of the outer 

 portion of the cheek is ornamented with transverse lamellose strias, more or less 

 curved and broken, but best developed towards the genal angle, where they run 

 obliquely across its posterior prolongation, but bend outwards near the jDosterior 

 margin. The inner portion of the cheek is ornamented by similar but shorter 

 lamellose broken strige, and they run in a different direction, being inclined almost 

 at right-angles to the other set. Tlie concentric strige, which were stated [op. cit.) 

 to ornament the border, really occur on the doublure, i. e. the lower surface of the 

 head-shield. 



The semicircular eyes, which are placed so far back as to touch the posterior 

 margin, are small, being less than one-fourth the length of the cheek, and are 

 situated on the summit of the inner convex portion at the inner posterior angle of 

 the free cheek. The shape of the free cheek of B. scotica and the absence of true 

 genal spines, the genal angle being simply produced backward, distinguishes it 

 from B. ardmiUanensis (oj). cit., pt. ii, p. 92, pi. xiii, figs. 1 — 4). But the above 

 characters of the free cheeks are closely similar to those of Bronteus htnatus, 

 Billings,^ and the other features of the head-shield and thorax so closely agree 

 that it is surprising to find the pygidia so dissimilar, particularly in the shape and 

 seofmentation of the axis. 



"O' 



Bronteopsis ardmiUanensis, Reed. Plate IV, fig. 7. 



1904. Bronteopsis ardmiUanensis, Eeed, op. cit., pt. ii, p. 92, pi. xiii, figs. 1 — 4. 



In my previous description of this species the pygidium had not been found in 

 1 Waller, ' Geol. Surv. New Jersey,' Palaeont., vol. iii (1902), p. 198, pi. xv, figs. 14—16, and 



references. 



