REMAINS OF EEPTILES AND FISHES. 115 



sharp prolongations are merely the ridges or keels described 

 above as extending from the apices downwards, seen still pro- 

 jecting after their base (the dentinal support) has been removed. 

 The same appearance is presented at the apex of the figure of 

 Aganodus imdatus, and strengthens our opinion of the nature of 

 that form. 



At the point of the largest spine of Ochlodus there is evidence 

 of two of those ridges or keels, one probably being a lateral 

 ridge, the other apparently the intermediate or dorsal one. At 

 the extremity of the small lateral siDuie, one of the strong late- 

 ral keels is well exhibited ; and the small central spine displays 

 distinct evidence of two keels. In many of our sections these 

 ridges assume the very same appearance which we see in this 

 figure ; and they are all found to be composed of enamel, as 

 these points are represented to be in Ochlodus ; and there can 

 be no doubt that the trace of enamel described and indicated at 

 g, on the large spine, is a lateral view of the keel, the lower 

 point of which terminates at g. 



We thus find that Ochlodus does not only agree in general 

 form, but even in the minutest details, with Diplodus ; and we 

 can find no distinguishing histological characters on which to 

 found this so-called genus. 



Ctenoptychius pectinatus, Agassiz. 



This species is not uncommon in the shales of Newsham and 

 Cramlington. One of the authors of this paper has a large suite 

 of specimens gathered at these localities ; they agree perfectly 

 well with C. pectinatus, though they usually have a greater num- 

 ber of denticles than represented in the figure in " Poissons 

 Fossiles." The number ranges from eight or nine to fifteen or 

 sixteen. Well developed specimens measure Jth of an inch wide 

 and a little less high. They are in the form of wide, flattened 

 plates, with the upper margin a little arched transversely and 

 denticulated, the denticles being rather obtusely pointed, come 

 from before backwards, and recurved ; the marginal surface is 

 concave behind and convex in front, and thickened posteriorly. 



