ASAPHUS (ISOTELUS) GRAYt?^:. 17 



Specific Characters. — Head-shield parabolic, slightly arched down at sides 

 posteriorly. Glabella hour-glass shaped, wide and well defined at base, contracted 

 between eyes, widening again in front, with sides arching out and following curve 

 of facial sutures, passing into obtusely rounded anterior end ; possessing decided 

 independent convexity at base and to level of eyes, but anteriorly flattened with 

 outline scarcely traceable and merging into general surface. Lateral lobes and 

 furrows absent ; but pair of small median tubercles situated on its surface just 

 behind level of eyes. No meso-occipital ring present. Axial furrows deep near 

 base, gradually decreasing in strength anteriorly, converging inwards to level of 

 eyes, but bending outwards in front of them and almost obsolete round front of 

 glabella. Fixed cheeks slightly arched down at sides, with gentle independent 

 convexity behind eyes, but forming narrow flattened band round anterior part of 

 glabella and scarcely separable from it. 



Facial sutures meeting anteriorly in pointed ogive, thence running outwards 

 and backwards at about 100° to less than half the distance to eyes, then curving 

 gently inwards to eye-lobes, and behind them running obliquely back in slight 

 convex curve to cut posterior border of head-shield at angle of about 45° and at a 

 distance from the axial furrows equal to half basal width of glabella. Maximum 

 distance between facial sutures in front of eyes only two-thirds that between them 

 on posterior margin of head-shield. 



Eyes small, elevated, situated behind middle of head-shield. Eye-lobes very 

 sharply bent up and rising high above general surface at angle of 45°-60°. Free 

 cheeks (see next page). 



Thorax (only detached segments known), with axis broad, over one-third width 

 of thorax, gently convex. Pleurae horizontally extended to fulcrum and beyond it 

 bent down strongly and slightly arched forwards ; extremity obtusely rounded ; 

 fulcrum sitnated at about one-third the length. Inner portion of pleura rather 

 convex, with strong sliglitly oblique furrow ; outer portion chiefly composed of 

 large triangular flattened or concave surface for articulation, bearing " Pander's 

 organ " at about half its length and near anterior edge. 



Pygidium parabolic, bluntly or acutely pointed behind, length rather greater 

 than width ; surface rather strongly convex from side to side. Axis only defined 

 by notches on anterior margin, more than one-third the total width of pygidium 

 apart, and with front end projecting slightly between them ; no trace of axis on 

 general surface. Axial furrows completely obsolete behind. Fulcrum situated 

 at about one-third width of pleural lobe from side of axis, with margin here 

 thickened and raised into sharp ridge running obliquely back to lateral margin, 

 cutting off large triangular articulating facet at anterior lateral angles of pygidium. 



Doublure very convex, about one-half width of pleural lobes, widening a little 

 posteriorly, and marked with numerous fine parallel equidistant striae slightly 

 oblique to margin. 



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