﻿CTENODONTID-E. 2iJ?) 



(t.) determine the anterior extremity of the specimen, and 

 suggest its probable reference to C. cristatus. Nearly all 

 the bones are considerably fractured on the external 

 surface, and some are shown in little more than impres- 

 sions ; but the approximate outlines of most of the 

 elements of the cranial shield appear to be distinguishable. 

 Hindermost is a large median plate (0) elongated antero- 

 posterior^*, and having the anterior margin produced 

 mesially into a short triangular projection between the 

 posterior extremities of the narrow pair of elements (I) 

 immediately in front. The last-named bones are only in 

 contact in the middle line of the skull for about half their 

 extent in advance of the process of the hinder mesial 

 element, being soon separated by another, though com- 

 paratively small and narrow, azygous bone (0) ; and this 

 likewise extends between the hinder ends of a second 

 larger pair (I), which would be originally in direct contact 

 with the anterior ends of the first pair. . This median 

 series of bones is immediately flanked by four pairs of 

 large broad bones, of which the first (II) and half of the 

 second adjoin the hindermost element, while the third is in 

 contact with both pairs of series I., and the fourth probably 

 with the anterior inner pair alone. Still more externally 

 there occurs another series of broad alternating bones on 

 either side (III), of which only few fragments are preserved. 

 On the whole, it will be noticed that there is a remark- 

 able resemblance to the arrangement of the plates in the 

 cranial shield of Bipterus (fig. 37), as already recognized 

 by Hancock and Atthey - ; the only striking difference 

 being the apparent subdivision of some of the elements in 

 the Devonian genus. Moreover, the median series of 

 bones is arranged exactly as in Aeipenser and Polyodon 2 . 



Purchased, 1885. 



38857. Crushed remains of the head ; Airdrie, Lanarkshire. The 

 dental plates are much abraded and imperfectly exposed ; 

 a few of the posterior cranial roof-bones are distinguish- 

 able ; and there are also portions of the palate, though 

 broken almost beyond recognition. Purchased, 1864 



45857. Operculum ; Newsham. Purchased, 1874. 



1 Nat. Hist. Trans. Northuinb. & Durham, vol. ir. p. 401. 



2 T. W. Bridge, Phil. Trans. 1878, p. 684, pi. lv. 



