INTRODUCTION. 



61 



there is no imbrication at all, and the edges meet 

 like plates or the flags of a pavement. But one 

 of the more remarkable contrivances for hold- 

 ing them in connection, is seen in some fossil 

 species, where the incumbent scale is furnished 

 with a hook, or tooth, which fits into a corres- 

 ponding hollow in the lower edge of the upper 

 scale, better understood by inspecting the accom- 

 panying cuts of those of (1) Paleoniscus* Freies- 

 Mteni) and (2) Pholidophorus\ macrocephalus y 



Agass. 



1. 2. 



The skin is immediately attached to the muscles, 

 the outer lateral layer of which will be seen in 

 the accompanying plate, (PL XXXI.) One 

 great muscle (a) occupies nearly the whole side, 

 and is almost the only one which is externally 



, ancient ; 



, oniscits. 



scale-bearing, like a snake* 



