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 
Bubstancj. The back is thickly spread with fructification ; the covers, fixed by 
their centres, seem to place it in the order Polypodiacese. The specimen is in 
shaly ironstone. 
I should like to send you samples of minute corals, &c., &c., from the Maestricht 
chalk. Yours respectfully, 
Hanley, Staffordshire, Ij- J- Abington. 
— The fossil of which a cast has been 
transmitted to us, is not a plant, but a 
portion of an icbthyodorulite or fin- spine 
of a carboniferous placoid fish described 
and figured by Agassiz, under the nijme of 
Gyracanthus tuberculatus. We subjoin 
a figure of the original specimen, also 
a fragment, 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 giooves 
extending obliquely downwards from the 
middle of the anterior face of the spine 
towards the posterior edges, and abutting 
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 
tame 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 : — 
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, M'Coy, Ann. Nat. His., 1848, pi. 2, p. 117. Carboniferous 
Rocks, Moyheeland, Ireland. 
Agassiz has suggested that the icbthyodorulite in question may have belonged 
to the same species as that he has described under the name of Gyracanthus 
formosn s the one being from the anterior dorsal and the other from the posterior 
dorsal fin. 
Gyracanthus tuberculatus. 
