§n lj)c Jfislj-|lcmains of il^t f ntotr 



Carkitifcrnus |locl\s of t\^t 



gristol gistrict. 



By a. J. HEATH, B.A., F.C.S., and C. LLOYD 

 MORGAN, F.G.S., Assoc.E.S.M. 



THE iish-remains of this district consist of teeth and 

 spines, the latter being known as IchthyodoruUtcs. 

 They belong to a group of the class of fishes termed the 

 CJiondroptcrygii, because of the cartilaginous or gristly 

 character of the skeleton of the fins, or Elasmohranclui^ 

 from the plate-like form of the gills ; and to a sub-group 

 termed Plagiostomij from the wide slit-like nature of the 

 mouth. 



Existing examples of the Plagiostome fishes are the sharks 

 and rays ; and since it is through them that we have some 

 idea of what the fishes of our carboniferous limestone were 

 like, it may be well briefly to describe some of their charac- 

 teristic features. The body is either cylindrical and taper- 

 ing at the ends, as in the sharks, or flattened from above 

 downw^ards (in technical phrase " depressed "), as in the 

 rays, of which the common skate is a familiar example. The 

 slit-like mouth is on the lower surface of the head, and is 



80 



