170 



ORDERS OF FISHES. 



Ctenodus, of the Devonian and Carboniferous, the scales are 

 oblong and imbricated, of a thin and delicate texture, with 

 a smooth central area bounded by concentric lines of growth. 



FMg. 536. — A, Diptents Valoicienncsii, reduced in size and restored — Old Red Sandstone 

 (after Pander) ; b, Front portion of the lower jaw of Dipterus platycephalus— Old Red Sand, 

 stone — viewed from above and showing the dental plates (after Pander) i c, Mandible of 

 Cienodus imhricatus, viewed from above, showing the dental plates, one-half of the natural 

 size, from the Carboniferous (after Hancock and Atthey). 



The skeleton is notochordal, and, as in Dipterus, enamelled 

 cranial plates are present, while the dentition is of the type 

 so characteristic of the latter genus. The lower jaw, namely, 

 carries a pair of elongated dental plates (fig. 536, c), the 

 upper surface of which is undulated by diverging ridges ; 

 and a corresponding pair of plates is attached to the roof of 

 the palate. The genera Holodus and Pcdccdaphiis of the De- 

 vonian formation, have likewise been shown by Traquair to 

 be referable to the Ctenodipterines ; and we may also place 

 here the Devonian genus Conchodus. 



LITERATURE. 



1. " Recherches sur les Poissons Fossiles." Agassiz. 1833-43. 



2. " Monographie des Poissons fossiles dii Vieux Gres Rouge." 



Agassiz. 1844. 



3. " FosKilen Fisclie des Silurisclien Systems." Pander. 1856. 



