NORTH STAFFORDSHIRE COAL FOSSILS. 2Lo 



in form from the typical specimen. It is probable that in 

 Pleuracauthus, as in existing sharks, there were teeth of 

 various sizes and forms, adapted to particular parts of the 

 mouth. The fortunate discovery of a specimen showing the 

 whole of the dental series would enable us to determine the 

 relationship of these various forms. Doubt has been ex- 

 pressed whether Diplodus Ag. is a tooth or a dermal tubercle. 

 Our own observations convince us that it is a tooth. We 

 have specimens showing patches of a granular cartilaginous 

 material, with a large number of teeth apparently placed in 

 rows in a part which no doubt was once occupied by the 

 head. 



Position and locality : Teeth are very common, especially 

 in the Rag mine and Deep mine ironstone shales, Fenton. 

 They are not uncommon in the Brown mine, Silverdale. 

 Fine specimens have been found in the Gubbin ironstone, 

 Shelton. 



Pleuracanthus (Diplodus) minutus. (Ref., Poiss. Foss., vol. 

 iii., tab. 22B, fig. 6 8.) This species is said to differ from 

 D. gibbosus by its small size. The lateral denticles are 

 slightly bent below and more arched at the summit, 

 and are longer in proportion to the size than in D. 

 gibbosus. No mention is made of the central denticle. The 

 figure given by Agassiz is too indistinct to enable us to make 

 out the number with certainty. There appear to be two 

 denticles in the centre. We have several specimens so dis- 

 tinguished. It is probable that this species is not distinct 

 from the last-named. 



Position and locality : Rag mine ironstone, Fenton. 

 Pleuracanthus IcevissimuSj Agassiz. (Ref., Poiss. Foss., 



R 



