NORTH STAFFORDSHIRE COAL FOSSILS. 217 



Longton ; Brown mine, Silverdale ; Cheadle coalfield. 



Gyracanthus tiiberculatus, Agassiz. (Ref., Poiss. Foss., 

 vol. iii., tab. 1, fig. 1 7). This species is very rare. In 

 form it differs but slightly from G. formosus. It is, how- 

 ever, distinguished from it by the ornamentation. Instead 

 of the ridges being zig-zagged, they are broken into elon- 

 gated tubercles which impart to the surface of the spine a 

 rasp-like appearance. Agassiz, in his description of this 

 species, suggests that it might have belonged to the anterior 

 dorsal and the preceding species to the posterior dorsal fin. 



Position and locality : Knowles ironstone, Fenton. 

 GEXUS ORTHACANTHUS, AGASSIZ. 



Orthacanthus cylindricus, Agassiz. (Ref., Poiss. Foss., 

 vol. iii., tab. 45). This is one of the rarest fin-defences 

 found in these coal-measures. Specimens have been found 

 eighteen inches or more in length. It is straight, circular in 

 section, and the base is hollow and generally filled with a 

 white powder. The surface of the spine is finely striated 

 longitudinally. The posterior or under side of the spine is 

 armed with a double row of closely-approximated thorn- 

 like spines, hooked downwards and extending from the 

 point to nearly half the length of the spine. 



Position and locality : Rag mine, Chalky mine, Knowles 

 and Deep mine ironstones, Fenton and Longton ; Brown 

 mine ironstone, Silverdale. 



Orthacanthus, sp. Our collection contains two fragments 

 of a spine which differs in several respects from the preceding 

 species. The spine is slightly bent ; a shallow cavity runs 

 Q 



