21G NORTH STAFFORDSHIRE COAL FOSSILS. 



Position and locality : Rag mine, Knowles and Chalky 

 mine ironstone, Fenton and Longton ; Brown mine iron- 

 stone, Silverdale. 



GENUS GYRACANTHTJS, AGASSIZ. 



Gyracanthus formosus, Agassiz (Ref., Poiss. Foss., vol. iii.,- 

 tab. 5, fig. 4 8). (See plate, fig. 3.) Fine specimens of this 

 defensive spine are not unfrequently found in these coal- 

 measures. Our largest specimen is about fourteen inches in 

 length, including about two inches of the base, which was 

 inserted in the flesh. It gradually tapers from base to apex 

 and is slightly bent. On the under side of the spine there 

 is a deep cavity which extends from the base to about two- 

 thirds of the entire length. The external surface is orna- 

 mented with ridges arranged in a zig-zag style, which cross 

 the sides of the spine obliquely and again unite on the 

 anterior margin. We have two varieties of this species, 

 one of which is smaller, more compressed, and the point 

 smooth and more rounded than the other. This is supposed 

 to have been a dorsal spine ; the other is supposed to have 

 been a pectoral spine. It is remarkable that nearly all these 

 spines have their points worn away at the side opposite to 

 that by which they were attached. The rubbing down of 

 the points favours the idea expressed by Sir Philip .Egerton, 

 that Ctenacanthus and Gyracanthus were fishes that lived 

 close to the more rocky parts of the ocean, the spines being 

 worn by rubbing against the rocks. One or two large, 

 flat, triangular bones have been found with the spines, 

 which are supposed to have been carpal bones. No specimen 

 has yet been found indicating the dentition of Gyracanthus. 



Position and locality : Not rare in the Rag mine and 

 Knowles ironstones ; fine specimens in the Ash coal shale, 



