32 TRILOBITES OF GIRVAN. 



base greater than length, moderately convex ; composed of median lobe and 

 three pairs of lateral lobes. Median lobe nearly semi-cylindrical, expanding a 

 little in front and also at base, slightly contracted between second pair of 

 lateral lobes ; anterior end obtusely rounded. Lateral lobes almost completely 

 severed from median lobe by strong longitudinal furrows; anterior lateral lobes 

 very minute or obsolete ; second lateral lobes subcircular to subtriangular, 

 swollen, detached, about one-fourth the length of the glabella; basal lateral lobes 

 subcircular, swollen, much larger than second pair, extending about two-fifths the 

 length of the glabella and with a width equal to about two-thirds that of base of 

 median lobe, with which they are connected by narrow depressed neck. Lateral 

 furrows deep, completely circumscribing lateral lobes, inclined to general axis at 

 about 45°, and united internally with longitudinal furrows. Axial furrows strong, 

 deep, converging anteriorly, arched outwards, but not in a regular continuous 

 curve, being bent in at second lateral furrows. Meso-occipital ring broad in 

 middle, subtriangular, being produced back into long, stout, straight, slowly 

 tapering horizontal spine as long as or longer than glabella; small tubercle situated 

 in middle of ring and small, subtriangular, indistinct occipital lobes behind basal 

 lobes of glabella. Meso-occipital furrow well marked, but weaker than glabellar 

 furrows, straight and horizontal in centre, but bent back behind basal lobes and 

 ending in deep pit on inner sides of occipital lobes. Fixed cheeks slightly arched 

 outwards, very narrow, but widening posteriorly to about half width of basal lobes, 

 forming long, swollen, rounded bands descending abruptly behind to depressed 

 neck-ring. Ocular ridges narrow, rounded, slightly arched outwards. Anterior 

 border of cranidium narrow, straight, flattened, slightly upturned, with deep pit 

 on each side in furrow. 



Free cheeks broad, very convex, wider than long, lateral edge strongly arched 

 outwards, with raised border armed with fringe of small spines. Genal angle 

 produced into long stout slowly tapering spine, projecting outwards and backwards 

 to eighth thoracic segment. Pleuro-occipital ring widening to genal angle. Eyes 

 situated far back, close to base of glabella, very prominent, being elevated on tall 

 vertical stalks. Facial sutures with anterior branches slightly convergent in front ; 

 posterior branches short, bending very sharply outwards behind eye to cut posterior 

 margin at acute angle. 



Surface of head-shield ornamented with tubercles of two or three sizes, 

 irregularly distributed. 



Thorax of ten segments. Axis narrow, cylindrical, convex, about one-fifth the 

 width of thorax ; rings with lateral nodules. Pleurse horizontal, straight, 

 produced into long free spines, increasing in length posteriorly, the last two 

 reaching back as far as tips of pygidial spines; each pleura composed of narrow, 

 flattened, depressed anterior and posterior band, separated by ^rong, elevated, 

 rounded central ridge ornamented with a few large tubercles, and prolonged into 



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