374 Messrs. Hancock & Atthey on Reptile- and Fish-Remains 



These sharp prolongations are merely the ridges or keels de- 

 scribed above as extending from the apices downwards, seen 

 still projecting after their base (the dentinal support) has been 

 removed. The same appearance is presented at the apex of 

 the figure of Aganodus undatus, and strengthens our opinion 

 of the nature of that form. 



At the point of the largest spine of Ochlodus there is evi- 

 dence 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 spine, one of the 

 strong lateral 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, Avith 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 at 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 number 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 one-quarter 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 den- 

 ticles being rather obtusely pointed, compressed from before 

 backwards, and recurved ; the marginal surface is concave 

 behind and convex in front, and thickened posteriorly, where 

 it is strongly defined from the base by a deep transverse con- 

 striction. A lateral section consequently presents a sigmoid 

 curve, the lower member of which is the larger and less bent. 

 The whole of the denticulated margin, including the denticles, 

 is coated with a thin layer of enamel, only traces of which can 

 usually be seen in sections. The base narrows suddenly im- 

 mediately below the denticulated margin, and is frequently 

 considerably longer than the upper glazed or enamelled por- 



