116 TRILOBITES OF GIRVAN. 



Society of Edinburgh ' (loc. cit.), and eight pairs of w ell-developed denticulated 

 spines can be easily recognised in the other figured specimens (Etheridge, op. cit., 

 pi. ii, figs. 7, 8). In A. Wage, "Wyville Thomson 1 described twelve to fourteen 

 lateral spines on the pygidium, but in one of his figures (fig. 4b) he shows 

 nine distinct pairs. In all the examples of A. grayx there are always two pairs 

 of spines posterior to those to which the pleural ridges run. 



Collections. — Mrs. Gray (f. M.) ; Edinburgh Museum ; Hunterian Museum. 



Horizon and Locality. — Balclatchie Group (Llandeilo) : Balclatchie. 



0. Acidaspis hystrix, Wyville Thomson, 1857. Plate XVI, figs. 3—5. 



1857. Acidaspis hystrix, Wyville Thomson (e.p.), Quart. Journ. Geol. Soc, vol. xiii, p. 207, pi. vi, 

 figs. 6, 9, 10 (nonftgs. 7, 8). 



1876. Acidaspis hystrix, Armstrong and Young, Cat. West. Scot. Foss., p. 15. 



1877. Acidaspis hystrix, Woodward, Cat. Brit. Foss. Crust., p. 19. 



1878. Acidaspis hystrix, Nicholson and Etheridge, Mon. Silur. Foss. Girvan, fasc. i, p. 123, pi. viii, 

 figs. 23—25. 



1878. Acidaspis lalac/e, Nicholson and Etheridge {e.p.), ibid., pi. viii, fig. 17 (non cet.). 



1899. Acidaspis hystrix, Mem. Geol. Surv., Silur. Eocks Brit., vol. i, Scotland, pp. 509, 672, 688. 



Specific Characters. — "Less than half an inch long. Glabella broadly triangular, 

 not very highly arched ; middle lobe rather narrow ; lateral lobes two, oval, 

 separated by distinct grooves from the central lobe and from the cheek ; basal 

 lateral lobe fused with the neck-segment. Portion of cheek within the facial 

 suture very gibbous, likewise confluent with the neck-segment. Neck-segment 

 very prominent, separated from the middle lobe of the glabella by a shallow 

 groove. . . . Head densely ornamented with tubercles. Axis of thorax and 

 abdomen narrow and prominent. Body-rings nine ; lateral portion of body-ring 

 horizontal, convex, with a groove running along it somewhat nearer the anterior 

 than the posterior margin, and dividing the surface into a narrower anterior and a 

 broader posterior ridge, the posterior ridge terminating in an abruptly reflexed, 

 slightly curved spine, nearly one third the length of the body, and the anterior in a 

 smaller spine, less abruptly reflexed and so placed as to pass below the posterior 

 spine of the segment before it. Tail minute, short, and as wide as the body-rings ; 

 axis of two very convex segments, margin fringed with twelve [fourteen] parallel 

 or slightly approximate equal spines. A ridge runs from the first axis-segment on 

 either side continuous with the antepenultimate spine, indicating the primary 

 spine, the posterior spine of the anterior tail-segment. The surface of the body- 

 rings and tail is richly granular." {Wyville Thomson?) 



1 ' Quart. Journ. Geol. Soc.,' vol. xiii (1857), p. 206, pi. vi, figs. 1 — 5. 



