94 TRILOBITES OF GIRVAN. 



have this post-axial ridge, and suggest in other respects also that they are referable 

 to Bronteopsis. 



Collection. — Mrs. Gray; Museum of Practical Geology. 



Horizon and Localities. — Balclatchie Group (Llandeilo) : Ardmillan ; Balclatchie. 



2. Bronteopsis scotica, Salter. Plate XIII, figs. 5 — 13. 



Bronteopsis scotica, Salter, MS. in Coll. Museum of Practical G-eology. 

 1879. Bronteopsis scotica, Nicholson and Etheridge, Mon. Silur. Toss. G-irvan, fasc. ii, p. 167, pi. x, 



figs. 21, 22 ; pi. xi, figs. 1—4 (?fig. 5). 

 1899. Bronteopsis scotica, Mem. Geol. Surv., Silur. Rocks Brit,, vol. i, Scotland, pp. 509, 514, 672, 688. 



Specific Characters. — Head broadly semicircular, with flattened curvature in 

 front ; weakly convex. Glabella clavate, broad in front, and reaching margin of 

 head shield, posteriorly narrowing regularly to base, which measures about two thirds 

 the anterior width ; moderately convex, most elevated towards middle ; feebly 

 marked off from cheeks along anterior half, but strongly defined from them behind. 

 Surface of glabella marked with three pairs of lateral pits, the first two pairs sub- 

 circular, generally shallow, faint and nearly obsolete, the posterior or basal pair 

 larger, deeper, and triangular in shape. Axial furrows strong behind middle of 

 glabella, but almost or quite obsolete in front. Occipital furrow wide and fairly 

 deep. Occipital ring narrow, rounded, and furnished with median tubercle. Fixed 

 cheeks with inner portion strongly convex, becoming flatter towards front margin; 

 wider at base than glabella. Facial sutures cutting front margin of head-shield 

 at about 100° — 120°, at a distance from the anterior lateral angle of the glabella 

 equal to about half its anterior width ; from this point, curving slightly outwards, 

 then bending gently inwards and encircling the small semicircular projecting eye- 

 lobe which is situated at about the level of the basal pair of glabellar pits. Behind 

 the eye-lobes the facial sutures bend outwards to cut the posterior margin of the 

 head-shield at a distance from the axial furrows rather greater than the basal 

 width of the glabella. Free cheeks triangular, with convex inner portion, sinking 

 down to broad concave concentrically striated border. Genal angles produced 

 backwards and broadly pointed. Surface of cheeks and glabella covered with fine 

 wavy, more or less concentric striae and raised lines. 



Thorax composed of seven or eight segments. Axis convex, cylindrical, about 

 two thirds the width of pleural portions. Pleurae narrow, horizontal, and straight 

 as far out as fulcrum which is situated at rather more than half their length ; 

 beyond fulcrum they are slightly recurved and bent down, and taper to a point. 

 A slightly oblique angulated ridge runs down each pleura, and on the anterior 

 edge is a narrow, rounded band. The extremities are transversely striated. 



