DAVIS : FOSSIL FISH EEMAINS. 
41 
Among'st the more frequent examples of ichthjodorulites 
found in the Mountain Limestone of Bristol, in which locality 
numerous specimens have been discovered, are the spines and 
teeth of large predacious fishes allied to the sharks now living*. 
Some of the fish-spiaes are of immense size. An example in the 
collection of Earl Ducie at Tortworth Court, which is imperfect at 
the base, was probably, three feet in length. The fish to which 
it belonged, judging by comparison with Hving forms, must have 
been nearly fort}^ feet in length. Many other genera and species 
of fishes which were possessed of large fin-defences occur in the 
limestone on the banks of the Avon. 
The limestone at Armagh, in Ireland, contains a large number 
of teeth, which fi-om their peculiar angular margins and flat 
surfaces, have evidently occupied the mouth of the fish with a 
flat pavement-like arrangement. Tiiis form of dentition is admir- 
ably adapted for preying on animals enclosed by hard shells like 
the mollusca. Perhaps the most characteristic teeth of the 
Yorkshire Limestones are those of Petalorhynchus and Pristodus, 
the dentition of the latter resembles that of the peculiar fish 
Diodon, now living in the seas under the warm rays of the tropical 
sun. In Diodoi), each jaw is occupied by a single tooth which 
extends over the palate as well as envelopes the outer margins of 
the jaws. 
Besides the fishes mentioned, which appear to be localized 
and peculiar to certain districts, there are many others which are 
common to all of them. Groups represented by the twisted teeth of 
Cochliodus, the pavement-like teeth of Psamniodus, and the sharp- 
pointed, shark-like teeth of Cladodus, are found in greater or less 
abundance in all the localities where fossil fishes have been 
discovered. 
The larger proportion of the fish -remains of the Carboniferous 
Limestone appear to be restricted to the formation ; they are not 
found in the earlier strata of the Old Red Sandstone or the still 
