NORTH STAFFORDSHIRE COAL FOSSILS. 211 



met with their death, whether by the introduction of some 

 noxious matter, or by some sudden catastrophe, we know 

 not, but the destruction of such an abundance of life as 

 is contained in this thin stratum must have been effected 

 by a cause of no ordinary description. 



Many of the genera and species found in these coal- 

 measures have a wide vertical range. Perhaps the most 

 common and widely-distributed genera are Megalichthys, 

 Caslacanthus, Rhizodopsis, Diplodus, and Palaeoniscus. 

 These genera occur in the uppermost beds and pass through 

 the whole series down to the lowest beds. Others again 

 have a restricted range, e. </., Cycloptychius and Mesolepis. 

 The former has only been found in the Deep mine ironstone 

 shale. 



Of the four divisions or orders into which Agassiz divided 

 the class Pisces, viz., the Placoid, Ganoid, Ctenoid, and 

 Cycloid divisions founded upon the form of the scales 

 the Placoid and Ganoid are the only orders found fossil 

 in the coal-measures. 



Of the Placoid order, about sixteen genera and more 

 than thirty species have been found in North Staffordshire. 

 The modern representatives of this order are the sharks 

 and rays, fishes for the most part covered with thick skin, 

 which in some members of the ray family is dotted with 

 tuberculated plates, or small bony points, such as are 

 found in the shagreen of the shark. The head is composed 

 of a single cartilaginous box, and is never found in a fossil 

 state. A very large portion of the extinct Placoids are 

 allied to Cestracion the Port Jackson shark. 



Many living Placoids have strong bony spines which 



