226 



LYELL'S ELEMENTS OF GEOLOGY. 



Ichthyodorulites. 



rivers and coasts. The teeth of a species of Acrodus, also, are 

 very abundant in the lias (Fig. 224.) 



Fig. 224. 



Acrodus nobilis, Agas. tooth ; commonly called fossil leach. 

 Lias, Lyme Regis, and Germany. 



But the remains of fish which have excited more attention 

 than any others, are those large bony spines called ichthyodo- 

 rulites (a. Fig. 225.), which were once supposed by some natu- 



Fig. 225. 



Hybodus reticulatus, Agas. Lias, Lyme Regis. 

 a. Part of fin, commonly called Ichthyodorulite. 

 6- Tooth. 



ralists to be jaws, and by others weapons, resembling those of 



the living Balistes andSilurus; but which M. Agassiz has shown 



to be neither the one nor the other. The spines, in the genera 



Fig. 226. ^ ast metinon ed, articu- 



late with the back- 

 bone, whereas there 

 are no signs of any 

 such articulation in 

 the ichthyodorulites. 

 These last appear to 

 have been bony spines 

 which formed the an- 

 terior part of the dor- 



Sal . fin > ^ ke tnat f the 

 living genera Cestra- 



CMmara monstrosa* 

 a. Spine forming anterior part of the dorsal fin. 



* Agassiz, Poissons Fossiles, vol. iii. tab. C. fig. 1. 



