154 



HISTORICAL PALAEONTOLOGY. 



highly characteristic of the Devonian of Britain and Europe, 

 and less so of that of America. In these curious forms the 

 head and front extremity of the body were protected by a 

 buckler composed of large enameled plates, more or less 

 firmly united to one another; whilst the hinder end of the body 

 was naked, or was protected with small scales. Some forms of 



Fig. 102. Fishes of the Devonian rocks of America, a, Diagram of the jaws and 

 teeth of Dinichthys Hertzeri, viewed from the front, and greatly reduced ; &, Diagram 

 of the skull of Macropetallchthys Sullivanti, reduced in size ; c, A portion of the en- 

 amelled surface of the skull of the same, magnified ; d, One of the scales of Onychodut 

 tigmoides, of the natural size ; e, One of the front teeth of the lower jaw of the same, 

 of the natural size ; /, Fin-spine of Machceracantfiua major, a shark-like fish reduced 

 in size. (After Newberry.; 



this group such as Pteraspis and Coccosteus date from the 

 Upper Silurian; but they attain their maximum in the Devo- 

 nian, and none of them are known to pass upwards into the 

 overlying Carboniferous rocks. Amongst the most character- 

 istic forms of this group may be mentioned Cephalaspis (fig. 

 103) and Pterichthys (fig. 104). In the former of these the 



