218 NORTH STAFFORDSHIRE COAL FOSSILS. 



along the posterior face, but its extent is not shown in 

 our specimens. Along the margins of the cavity there are 

 a number of blunt, elongated tubercles. The surface of the 

 spine is thickly strewn with fine punctures. 



Position and locality : Rag mine ironstone, Fenton. 

 GENUS CTENOPTYCHIUS, AGASSIZ. 



Ctenoptychius apicalis, Agassiz. (Ref., Poiss. Foss., vol. 

 iii., tab. 19, fig. IA). (Harpacodus apicalis, Ag. MSS., 

 June 27, 1859). (See plate, fig. 12). This species was 

 named by Agassiz from specimens collected at Silverdale. 

 The crown of the tooth is transversely oval, the upper 

 edge semi-elliptically rounded and divided into eight or more 

 acutely-pointed vertical lobes ; the central lobe is the highest, 

 those on each side gradually diminishing in size as they 

 proceed to the exterior. The inner surface of the crown is 

 smooth, and apparently concave. This appearance arises 

 from the imbricating fold which projects beyond the root 

 of the crown, and which divides the root from the base. 

 This fold is slightly arched downwards and apparently double. 

 What renders some of these teeth so remarkable is, that on 

 the inner surface of the tooth, the fold which divides the 

 base from the crown bears upon the border a row of 

 acutely-pointed denticles : behind this, and standing above 

 it, there is a second row : each contains about eighteen 

 denticles unequal in size. This form of tooth is rare and 

 probably belonged to the front of the mouth. The base 

 of the tooth is broader than the crown and equal in height. 

 We have several specimens of teeth which differ from those 

 figured by Agassiz. These, probably, only differ according 

 to the position they occupied in the mouth. 



