1858.] HtTXtEY— STAGONOLEPIS. 443 



a centre which lies about the junction of the anterior two*fifths with 

 the posterior three-fifths of the whole ornamented surface. A small 

 marginal space, laterally and posteriorly, is, as Prof. Agassiz has 

 observed, free from sculpture (fig. 1). 



An inch and a quarter transversely, by a little less antero-poste- 

 riorly, is a fair statement of the average dimensions of these flat 

 scutes, of which I have only seen one or two detached impressions 

 among the more recently discovered remains of Stagonolepis. 



The angulated scutes may be roughly divided into three kinds : 

 the hroad, the thick, and the irregular. 



The hroad angulated scutes (fig. 2) have a transversely elongated 

 trapezoidal form, — one of the short sides, which it will appear is the 

 outer, not being parallel to the other, but sloping obliquely outwards 

 and forwards. The largest of these scutes which I have seen is a 

 well-preserved specimen from Lossiemouth, which, with the excep- 

 tion of a very small portion of its anterior and inner edge, is entire*. 

 The anterior edge has a length of 4|- inches ; the posterior of 4| 

 inches. The length of the scute in the middle line is 2^ inches. 

 The inner edge is straight ; the outer, somewhat convex behind and 

 concave in front, passes into the produced antero-external angle. 

 The inner sui'face only of this scute was visible, but, by cutting away 

 a portion of its substance, the ornamentation of the outer surface 

 and its natural cast in the sandstone came into view, so that the 

 relations of both surfaces could be observed. The contour of the 

 outer surface is somewhat concave from before backwards, and the 

 anterior edge of the scute is bevelled as in the flat scutes; the 

 articular facet (a) thus formed is mder externally and internally 

 than in the middle. 



About If inch from the inner edge, and therefore much nearer 

 the inner than the outer, a strong longitudinal ridge apj)ears upon 

 the scute, and, rising posteriorly, ends upon the hinder edge of the 

 bony plate in a sort of rudimentary spine (6), while anteriorly it gra- 

 dually dies away. The outer face of the scute falls away rapidly 

 on each side from the ridge, so that, while measured through the 

 ridge, the posterior margin of the scute is y^ths of an inch thick, at a 

 distance of three-quarters of an inch from it, on the outer side, it 

 measures hardly more than ith of an inch, and is but little thicker 

 at a like distance on the inner side. 



The outer surface of this wide angidated scute is sculptured in the 

 same way as that of the flat scutes, but the pits are larger, and the 

 marginal ones are so much elongated as almost to deserve the appel- 

 lation of grooves. The posterior, most prominent part of the ridge, 

 is devoid of sculpture. The inner surface of this and of other scutes 

 of the same order is quite smooth, except posteriorly, where it pre- 

 sents a fine transverse striation ; and its contour is totally different 

 from that of the outer surface. Transversely it is concave, each side 

 sloping towards a longitudinal valley, which corresponds with the 



* I have since seen a specimen of one of these scutes 5J inches wide by 2| 

 inches long. — ^July 5th, 1859. 



