On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 463 
described by Prof. M‘Coy in Brit. Palzeoz. Foss., p. 643, but no figure is given of 
it. Itis described as trapezoidal: lateral sides long, straight, equal ; posterior 
side shorter than the lateral ones and concave; anterior side shortest, slightly 
convex. This is the description of a tooth longer than broad, whilst the one 
figured by Portlock is considerably broader than long. 
In June, 1859, the late Prof. Agassiz visited this country, and devoted much time to 
a re-examination of the large collection of palates trom the Mountain Limestone, 
which form a conspicuous element in the collection of fossil fishes gathered by the 
Earl of Enniskillen. 
The genus Psammodus amongst others received the attention of that skilled 
Ichthyologist and the species P. cornutus was justly eliminated from the genus. 
During the twenty years subsequent to the publication of the great work on Fossil 
Fishes by Agassiz, numerous additions had been made to the collections of 
Carboniferous Limestone fish remains, and consequently improved opportunities 
for their study and determination were available. The teeth hitherto included in 
the genus Psammodus, which were named P. cornutus in the “Poissons Fossiles” but 
were undescribed, were discovered to be not only of distinct generic character, but 
to represent more than one genus of fishes. Prof. Agassiz rearranged the several 
specimens, and appended to them new generic and specific names, intending at 
some future opportunity to publish descriptions and plates of them,-with a general 
revision of the whole group of fish remains from the Carboniferous Limestone. 
Unfortunately this opportunity did not occurr, and the death of Professor Agassiz 
has now rendered it impossible. The determinations and nomenclature of Agassiz 
are here adhered to and retained, or when any change appeared necessary it has 
been duly noted and explained. 
The specimens comprised in the several genera indicated by Prof. Agassiz are 
comparatively numerous in the Limestone quarried near Armagh; but notwith- 
standing a few specimens have been obtained, they are very rarefrom other localities ; 
a large majority of the species are represented by a fairly numerous set of examples, 
‘and in no instance are they founded on unique specimens. 
In some respects they approach the Psammodont group of fish palates, they were 
more or less flat and pavement-like in their arrangement ; but as to the details of 
that arrangement there is little orno evidence, The teeth of Copodus cornutus, Ag., 
which in many respects must be considered the type of the group, have been found 
associated in pairs; they are very divergent in form. Whether, a large or small 
number of teeth were implanted on each jaw is undetermined ; it is necessary to 
await the advent of more complete examples, and should such be discovered, it is 
quite possible that a considerable rearrangement of the genera and species which 
are included in the group may be found necessary. At the present moment the 
genera appear well defined and established on a sound basis, but the whole course 
of paleeontological research has proved that the ideas conceived of genera and species 
TRANS. ROY. DUB. SOC., N.S., VOL. I. 4C 
