BRITISH FOSSILS 



Decade the Twelfth. 



ILLUSTRATIONS OF THE STRUCTURE OF THE 

 CROSSOPTERYGIAN GANOIDS; 



BY 



Thomas H. Huxley, F.R.S. 



I. — The genus Glyptopomus. 



At p. 57 of the "Poissons Fossiles du Vieux Gr&s Rouge," 

 Prof. Agassiz remarks, in establishing this genus, that he at first 

 took the only specimen known to him for a Platygnaihus ; and it 

 is figured in the 26th plate as Platygnaihus minor. He de- 

 scribes the unique specimen of Glyptopomus minor in the following 

 terms: — " 



" This fish, of which I know but a single specimen, obtained at 

 Dura Den, and placed in the collection of Prof. Jameson, has the 

 body wide and heavy, and resembling in form that of Holoptychius. 

 It lies on its belly, and is turned a little to the left side, so that it is 

 the back and right side which are visible. The head is proportion- 

 ably small, and composed of enamelled and irregularly sculptured 

 bones, which appear to be covered with a thick and very variable 

 granulation. In the middle of the head it is easy to distinguish 

 the frontals ; in front, the nasals ; behind, the occipital ; and a great 

 lateral enamelled plate, which indicates that the cheek was 

 covered, as in Polypterus, by a single osseous lamella, below which 

 the great masticatory muscle was fixed. 



" The scales of the body are very considerable, very high on 

 the sides, almost square on the back. They form oblique series, 

 which meet at an acute angle in the middle line of the back. The 

 scales themselves are very thick, placed side by side, apparently 

 connected together only by the integument in which they were 

 implanted. Their enamelled surface is not smooth, but adorned 

 with a fine granulation, which gives them a velvety aspect. I 

 have been unable to examine their microscopic structure. 



" Only a few traces of fins are preserved in the specimen figured ; 

 probably a portion of the ventral near the throat, and a vestige of 

 the dorsal, or caudal, near the end of the tail. The fin rays seem 

 to have been short and delicate." 



In the " Preliminary Essay " of the " Tenth Decade" I de- 

 scribed and gave a woodcut of the skull, represented in Plate I., 

 fig. 2, of the present decade ; and in a note at the end of that 



a 2 



