534 



THE GEOLOGIST. 



It may be common in other places, but I have not access to any work in which it is 

 described. Will you favour me with the name of it ? 



I have also found a portion of a large leaf of a fern, having a strong midrib : 

 simple, undivided, like the hart's tongue, and which was probably of a leathery 

 sub«tanc.\ The back is thickly spread with fructification ; the covers, fixed by 

 place it in the order Polypodiaceae. The speci 



their centres, seem to pU 

 ehaly ironstone. 



I should like to send you samples of minute corals, &c., &c. 

 gjjalk. Yours respectfully, 



Hanley, StafiFordshire, 



specimen is in 

 from the Maestricht 

 L. J. Abington. 



— The fossil of which a cast has been 

 transmitted to us, is not a plant, but a 

 portion of an ichthyodorulite or fin- spine 

 of a carboniferous placoid fish described 

 and figured by Agassiz, under the name of 

 Gyracanthus tuberculatus. We subjoin 

 a figure of tbe original specimen, also 

 a frograent, both base and apex being 

 broken off. 



The generic characters of the ichthyo- 

 dorulites of the genus Gyrocanthus consist 

 especially in the disposition of the oblique 

 wrinkles which ornament their surface ; 

 these consist of ridges and deep grooves 

 extending obliquely downwards from the 

 middle of the anterior face of the spine 

 towards the posterior edges, and arbutting 

 on the sides of the median line posterior 

 to the longitudinal grove. Variations of 

 form and of sculpturing may result from 

 the position of these rays in the anterior 

 or posterior dorsal fin ; and as fragments 

 of cartilaginous fish are found in the 

 same beds with the spines upon which 

 the genus Gyrocanthus is founded, such 

 probably belonging to the same species. 

 Diligent search should, therefore, be 

 made for all fish remains found in the 

 same strata from which our correspondent 

 obtained his specimens. 



The following are the ichthyodorulites 

 of this genus hitherto figured : — 



Gyracanthus tuberculatus. 



I. Gyracanthus formosus (Poiss, Foss., Vol. III., Tab. 5, f. 2-6), Coal Measures 



of Newcastle- on-Tyne, Sunderland, Alnwick in 

 Northumberland, Dudley, Worcestershire. Freshwater 

 Limestone of Burdie House 



II. G. ornatus (Poiss, Foss., Vol. III., Tab. la, f. 1-7), Coal Measures, Sunderland. 

 IV^. G. Alnwicensis (Poiss, Foss., Vol. III.," Tab. la, f. 8), Coal Measures, 



Alnwick. 



V. G. obliquus, Al'Coy, Ann. Nat. His., 1848, pi. 2, p. 117. Carboniferous 

 Rocks, Moyheeland, Ireland. 

 Agassiz has suggested that the ichthyodorulite in question may have belonged 

 to the same species as that he has described under the name of Gyracanthus 

 formosus ihQ one being from the anterior dorsal and the other from the posterior 

 dorsal fin. 



