ILLiENUS. 



191 



The head forms a regular quarter of a sphere, and is very equally and highly convex ; 

 it is marked for one third up by axal furrows, which first converge a little, and then 

 turn outward above the oval gland. Eye distant from the glabella about half the width 

 of the latter, of moderate size, and placed at less than its own length apart from the 

 neck margin. Cheeks broad, with rounded angles — the facial line divergent above the 

 eye. No neck-furrow, even in the cast. 



Thorax with its axis nearly parallel-sided, a good deal wider than the pleurae, and very 

 convex, separated (in the cast, at least) by a broad, flat-bottomed furrow ; the pleurae 

 convex thence as far as the fulcrum, which is placed at one third out in all the rings ; the 

 pleurae bent down and a good deal backwards from the fulcral point ; the ends pointed, 

 and curved backward (they are straight in //. Bowmanni) . 



The tail a long half-oval, broader than long, and not obtuse at the tip ; the front 

 margin uneven, divided into a broad axal lobe much arched forward, which is distinctly 

 marked out by axal pits, but no axal furrows. Thence to the fulcrum the margin is 

 straight, and beyond it a wide oblique truncation, with the edge of the facet vertical. 

 No axal furrows or depressions interrupt the smooth contour, except at the extreme 

 front margin. 



Our figured specimen shows (the cast being broken) a very broad and remarkably 

 bent fascia beneath, extending near half-way up the tail, and divided into two very 

 distinct portions. The outer part is narrower and 

 only slightly concave round the hinder margin 

 (Fig. 48 a) ; but at the upper angles (in Fig. 48 b) 

 this part becomes first flat, and then strongly con- 

 cave ; and thence bends upwards, with a sharp 

 angle (making a deep furrow on the cast) between 

 it and the inner half of the fascia. This inner 

 portion is then reflected closely beneath the upper 

 surface, and follows it. The squamous lines 

 which cover the inner half are wide apart ; those 

 on the marginal portion closer together. Round 

 the extreme edge the fascia forms a convex fillet, 



so that the section of the whole fascia, very perfect in this specimen, would be somewhat 

 like our figure 48. The variations of the caudal fascia deserve close study; but the 

 •details of its shape are better understood by a figure than description ; a circumstance 

 not at all uncommon in natural-history illustration. 



Locality. — Ll.vndovery schists of Mullock, Girvau, Ayrshire (Prof. Thomson's 

 and Mr. Wyatt-Edgell's cabinets). 



Fig. 48. 



Section of the tail, with its incurved fascia : a, 

 longitudinal section ; b, transverse section 

 across the facets (* *). 



