FISH-REMAINS OF THE CARBONIFEROUS ROCKS. 83 



Passing now to the remains of fishes found in tliese lower 

 carboniferous rocks in the Bristol district, we rnay first take 

 notice of the teeth. There are certain primitive elasmo- 

 branchs in which the vertebral column is not clearly divided 

 Tip into distinct vertebrae, and to which the name Ichfhyo- 

 tomi is applied by some authors. To this group belong the 

 genus Pleur acanthus^ the remains of which have been 

 found in some abundance in the North of England and Scot- 

 land, but are not found in this district. A second genus, 

 belonging to a different family, the Cladodontidce, has 

 afforded teeth which consist of a central sharp, flattened 

 cone, flanked on either side by smaller points. This genus, 

 Cladodus, seems to have had a broad and depressed head, 

 in the jaws of which the teeth were arranged in several 

 rows. A Cladodus tooth was found some years ago in the 

 millstone grit at Long Ashton by Mr. Dallas, who was then 

 curator of the Bristol Museum. Other specimens have been 

 found in the carboniferous limestone. Tliese primitive forms 

 are by some palaeontologists regarded as early forms of sela- 

 chians, to which the name Proselachtl is by them applied. 



To this group, perhaps, belongs the family of the CocliUo- 

 dontldce^ of the teeth of which Sn^ Richard Owen remarked 

 in 1867 that " it would seem as if the several teeth of each 

 oblique row in Cestracion [the Port Jackson shark] had been 

 welded into a single mass." The Cochliodont teeth were 

 formed in a continuous curved plate, sometimes with a smooth 

 crown, sometimes with one marked with grooves and ridges, 

 which seem to indicate the separate factors of the compound 

 tooth. Additions seem to have taken place at the inner 

 borders, while the outer borders curved round continuously 

 instead of becoming detached. The genera belonging to this 

 family which are represented in our limestone are Strchlodus^ 

 FsephodiiSj CJiomatodus, Tomodns^ Deltodits, DcUopfychms, 



