528 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
The Ichthyodorulites described by Prof. Agassiz, and included in the genus 
Oracanthus have the following characters in common. Oracanthus pustulosus 
and O. milleri ave very broad in comparison to their length; the external bony 
part is extremely thin and the internal cavity excessively large ; they are laterally 
compressed, acutely pointed, and the basal portion, unlike other genera of the 
Plagiostomata, is covered to the extremity with the same external ornamentation 
which is characteristic of the exposed surface, there being no evidence that any 
part of the base was implanted in the integuments of the fish. The difference 
between the two species consisting in the style of ornamentation, O. pustulosus 
being studded with tubercles arranged indiscriminately over the surface, whilst on 
O. milleri, the tubercles were extended in oblique rows across the surface or 
closely approximated, they formed oblique ridges. Oracanthus confluens, which 
Prof, Agassiz named in manuscript from specimens in the Enniskillen collection, 
was found at Armagh, the two previously mentioned being from the Bristol Lime- 
stone. O. confluens may be distinguished from 0. pustulosus and O. milleri by the 
extreme width of its base. An example measuring 3:3 inches on its shorter side, 
between the point and the base, is 3°0 inches across the base, so that the width 
of the base is nearly equal to the length, whilst in O. millevi the length from point 
to base is more than double the basal diameter. The surface is covered with 
pustulations which in some specimens assume a definite arrangement, or form ridges 
by the coalescence of the tubercles, whilst in others there is no definite arrangement. 
Specimens exist which exhibit modifications embracing both these forms. 
The type specimen of Oracanthus minor, Ag., which forms a part of the Jones 
Collection in the Museum of the Geological Society, at Burlington House, is also from 
the Armagh Limestone. Except a quarter of an inch of the upper extremity the 
actual specimen has not been preserved, and there is only its impression on the 
matrix left: It is represented in the ‘“ Recherches sur les Poissons Fossiles,” Vol. 
TII., Plate iii, fig. 5. Tt is quite different in form to the other species already 
mentioned, and the small portion preserved is not only tuberculated, but very 
distinctly striated, the strize being parallel with the length of the spine, and the 
tubercles situated in the grooves between the ridges. The latter feature 
distinguishes it from Oracanthus, and the general appearance of the spine appears 
to indicate a near, if not identical, relationship with Asteroptychius, Ag. From 
the above, it may be gathered that the species of the genus Oracanthus, depending, 
ag they do, on the characters of the surface ornament, are not of sufficent stability 
to justify retention, and that one species, O. minor, Ag., must be eliminated from 
the genus. 
Having thus briefly reviewed the position with regard to the hitherto described 
species of Oracanthus, it is proposed to suggest a reconstruction of the genus, which 
will, in all probability, entail its removal from the Plagiostomata and its inclusion 
in the Placodermic Ganoids. 
The figures on Plate LXIL, represent a series of specimens, all obtained from the 
