new Species o/'Gyracanthus. 



373 



the posterior edge of the spine, this surface is smooth. At 

 the angle formed by the junction of the posterior with each 

 lateral surface there is a row of sharp recurved denticles ; 

 they are small and closely set, being not more than l-20th 

 of an inch apart, and projecting about an equal distance from 

 the spine. The two rows of denticles extend from the point 

 along at least half the length of the spine. 



Spine of Gyracanthus denticulatus, | nat. size. 

 1. * 



1. Upper half of spine. 



2. Basal extremity. 



This spine presents features differing very materially from 

 the species of Gyracanthus hitherto described. In general form 

 and outline it is similar to Gyracanthus formosits, Ag.*, except 

 that it is much compressed laterally and of a more delicate 

 and elegant mould. It, however, differs materially from the 

 types of Agassiz, as well as all others, in having a double 

 row of denticles along the dorsal aspect. Prof. M'Coyf has 

 described a species of Gyracanthus from the Yellow Sandstone 

 at the base of the Carboniferous series near Draperstown, 

 which has indications of a small number of denticles near the 

 apex ; it is named obliquus, and is rounder and more robust 

 than the one here described ; it has not the smooth space 

 near the apex ; and the denticles appear to be of quite a diffe- 

 rent form, besides being so limited in number and extent. 

 I suggest the specific name denticulatus, as serving to distin- 

 guish the special features of the specimen now described. 



Locality. Tingley, near Leeds. In an impure cannel 

 coal of the Middle Coal-measures. 



* Poissons Fossiles, vol. iii. p. 17, tab. v. figs. 4, o, 6, 7, 8. 

 t Brit. Palteoz. Bocks and Foss. p. 629, pi. 3 K. figs. 13, 14. 



