BEITISH FOSSILS. 



3 



rounded and slightly emarginate. A broad shallow furrow runs 

 round the end and sides, leaving only a small central convexity of 

 the same shape as the hypos tome ; this convexity is not indented 

 by any lateral furrows. 



The surface of the head is covered by a fine close granulation 

 (fig. 11), which occupies also the free cheeks or wings (fig. 5) ; it is 

 therefore one of the generic distinctions from Cheirurus, in which 

 the cheeks are always pitted or scrobiculate. 



Thorax parallel sided, scarcely tapering backwards, of 11 thick 

 rounded rings ; the axis as wide as the sides, and of equal breadth 

 throughout, very convex ; each joint much raised and rounded (see 

 fig. 10). Pleurae horizontal as far as the fulcrum (fig. 7, a), and then 

 abruptly deflexed, and from this point the pleura tapers outwards to 

 a conical blunt point, which at the extreme tip is a little bent 

 forwards. The fulcrum is placed at rather less than half-way from 

 the axis, but in the last segment (fig. 8) it approaches much nearer, — 

 to about one third. Its place is indicated by a protuberance both 

 on the forward and hinder edge of each segment (fig. 7, a and h), but 

 these swellings are not isolated tubercles as in Cheirurus, nor are 

 there any oblique or longitudinal farrows on the pleurae, as in that 

 genus, to break up the uniform convex surface of the segment. 



Tail about semicircular, truncate ; the axis conical, its base of two 

 depressed close-set rings, its apex of one long triangular joint, which 

 is separated from the second joint by a deep depression ; from thence 

 it is flattened, or even depressed for some distance, but suddenly 

 rises to an obtuse and elevated tip (fig. 9, a); which, seen sideways, 

 presents the appearance represented in fig. 2, where a is the obtuse 

 tip of the axis. The sides are composed of three obtuse convex 

 lobes which scarcely project on the margin ; the upper one follows 

 the bend of the hindermost pleura, the second is less curved, the 

 third parallel to the axis ; all are deflected so that an end view ol 

 the tail (fig. 13) presents an angular figure. 



The entire surface of the thorax (fig. 10) and tail, like that of 

 the head, is covered with a fine granulation, the grains of equal 

 size throughout. 



Variations. — Our Dudley specimens have the tail somewhat 

 shorter and wider, and the terminal joint of the axis therefore 

 shorter, than those from Bohemia. Irish specimens (figs. 14, 15) 

 are more like the foreign ones in this respect. The space between 

 the lower glabella lobes is least in these Irish specimens, though 

 some of them have it consideraby wider than the diameter of the 

 lobes ; in a Wexford specimen, the space is proportionally as wide 



