226 



LYELL'S ELEMENTS OF GEOLOGY. 



Ichthyodorulites. 



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

 very abundant in the has (Fig. 224.) 



Fig. 224. 



Acrodus nohilis, 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. a b 



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 and Silurus ; but which M. Agassiz has shown 

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

 p. ^^^^ metinoned, articu- 



^* ' a, ^ ^^t'^ 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- 

 r,,- . * sal fin, like that of the 



ChimcBra vionstrosa.* . . ' 



a. Spine forming anterior part of the dorsal fin. living genera Cestra- 



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



