﻿ASTEK0LEPID.1S. 



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elements, the anterior (a.m.d.) larger than the posterior (p.in.d.) ; 

 and these are bounded by two dorso-lateral pairs (a.d.L and p.d.l.), 

 of which the hinder is much the largest. There are two pairs of 

 ventro-lateral plates (a.v.l. and p.v.l.), which meet in the mesial line 

 below, and are sharply reflexed upwards at the sides to overlap the 

 inferior edge of the dorso-laterals ; while on the ventral surface 

 there occurs a small, median, diamond-shaped space between the 

 inner truncated angles of these plates, filled by a much-overlapped 

 median ventral (m.v.). The slightly excavated front border of the 

 anterior ventrolaterals is filled by a pair of small semilunar plates 

 (s.l.) tapering outwardly ; and again in advance of these is a pair of 

 much larger, transversely elongated elements (mn.), concave above, 

 which have been termed mental by Traquair. The latter plates are 

 loosely fixed and often displaced (see PI. V. fig. 3, mn.), but can 

 scarcely be interpreted as a mandible. At a point somewhat in 

 advance of their hinder extremities, the posterior ventro-lateral 

 plates are distinctly constricted, with an inner transverse thickening ; 

 and this may mark the termination of the abdominal cavity. 



Near their front extremity the anterior ventro-lateral plates are 

 strengthened by a robust transverse ridge on the visceral aspect, 

 and close to this the pectoral appendages are fixed by a most 

 complex, ginglymoid articulation. Each appendage is completely 

 encased in closely-fitting plates ; and a large orifice in the 

 supporting articular facette bears witness to the passage into its 

 interior of well-developed vascular canals and nerves. A powerful 

 articular plate (ar.), with rounded proximal end, occurs both on the 

 dorsal and on the ventral aspect of the appendage ; an inner and 

 an outer marginal (w.), with an upper and a lower median anconeal 

 plate («.), are closely united with these, and at the distal extremity 

 of this group of plates the appendage is jointed. The distal 

 segment is shorter and smaller than the proximal, consisting of an 

 upper and lower central piece (c.J, a pointed terminal plate (u\ and 

 two pairs of marginals (m.). 



The tail is comparatively small, covered with imbricating rounded 

 or hexagonal scales, with a series of large azygous ridge-scales on 

 the dorsal aspect. The body-scales are thin and finely tuberculated 

 (see Nos. P. 3209, P. 4036), while the dorsal ridge-scales are 

 comparatively robust. The latter are interrupted shortly behind 

 the posterior median dorsal plate by a small triangular dorsal fin ; 

 this being membranous, and only stiffened on its front margin by one 

 (or perhaps two) of the scales, which might be mistaken for a spine. 

 Behind the fin, the ridge-scales are very deeply imbricating to the 

 extremity of the tail, which is somewhat upturned (PL V. fig. 5), 



