ACIDASPIS GIRVANENSIS. 33 



long, stout, backwardly directed spine, with finely tuberculated surface; spines 

 successively increase in length and become parallel to axis of body ; anterior band 

 of pleura ornamented with 6 — 9 small closely set tubercles. 



Pygidium transverse, with rounded border, and four pairs of long marginal 

 spines; anterior edge raised and ending laterally in short marginal pointed 

 projections. Axis composed of two rings Avith a small terminal piece. Pleural 

 lobes flattened, traversed by oblique ridge from first axial ring to base of second 

 pair of marginal spines. Marginal spines straight, parallel, equidistant ; first 

 pair short; second pair the longest and the stoutest; third pair of same length 

 as first ; fourth pair equal in size to third pair. Surface of pygidium and spines 

 covered with small tubercles rather closely set. 



Dimensions. — 



Length of glabella .... 4*0 mm. 

 Width of ,, at base . . . 6*0 ,, 



Length of meso-occipital ring and spine . . +5"0 ,, 



Remarks. — One small but nearly complete individual, one cranidium with the 

 occipital spine, a head-shield with the free cheeks and tall eye-stalks, and two 

 pygidia constitute the material from which the above description has been 

 drawn up. 



The general characters of the head recall A. hrighti, Murchison,^ and A. grui/i, 

 Barrande^ (non A. grayse, Etheridge). The pygidium and thorax closely resemble 

 A. coronata, Salter.^ 



Horizon and Locality. — Starfish Bed, Drummuck Group (U. Bala) : Thraive Glen. 



Acidaspis girvanensis, sp. nov. Plate V, figs. 8 — 10 ; Plate VI, figs. 1 — 3. 



Specif c Characters. — Head-shield transverse, broadly semi-elliptical, strongly 

 convex from back to front and less so from side to side. Cranidium with nearly 

 straight anterior edge projecting slightly in front of free cheeks ; free cheeks 

 large, subtriangular, arched downwards on each side, with genal angles furnished 

 with long spines. Glabella ovate ; with subcylindrical, swollen median lobe, 

 truncate anteriorly and expanding slightly so as to overhang laterally ; three pairs 

 of lateral lobes present, all completely circumscribed by furrows ; anterior pair of 

 lobes very small, forming minute subcircular nodules ; middle pair subcircular or 

 oval, slightly oblique, about a quarter the length of the glabella ; basal pair large, 

 oval, pointed anteriorly, projecting outside base of middle pair, nearly half the 

 length and fully a quarter the width of glabella. Axial furrows deep, gently 

 arched outwards, forming a regular curve, converging anteriorly and ending in a 

 deep pit in front. 



1 Lake, ' Quart. Journ. Geol. Soc.,' toI. Hi (1896), p. 236, pi. vii, fig. 5. 



2 Barrande, ' Syst. Silur. Bolieme,' vol. i, p. 751, pi. xxxix, figs. 20, 21. 

 * Lake, op. cit., p. 237, pi. vii, fig. 6. 



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