48 
DAYIS : FOSSIL FISH EEMAINS. 
seem to lie in the direction of the Plagistomata, is very abundant in 
the upper bed of the series and is pecuHar to this district. 
In other localities the group HyhodontidcB is represented by 
several g-enera of spines which bear a g-reater or less resemblance 
to the Hybodus of the Lias. Amongst the most formidable of 
these are the spines of Ctenacanthus and associated with them 
the teeth called Oladodus. It has been thought probable, from 
the spines of Ctenacanthus and the teeth of Cladodus occuring 
together with considerable frequency, that they may have 
been co-existent in the same fishes. It is well known that the 
spines of Hybodus of the Lias were associated with teeth to 
which Cladodus bear some resemblance. The latter differ from 
Hybodus in the cusps produced from the surface of the crown 
being longer and sharply pointed ; in other respects they are 
similar. A peculiar circumstance in connection with this group 
in the Yorkshire Limestone is that, whilst the teeth of Cladodus 
are represented by five or six species, some of which, like C. strait- 
us, are very common ; there has hitherto been no specimens of 
Ctenacanthus discovered. The teeth occur in the thick-bedded 
limestone of Settle and Giggleswick, examples from the quarries 
in the neighbourhood may be seen in the Museum of the Grammar 
School of the latter place ; they also frequently occur in some 
of the thin limestones in Wensleydale, comprised in the Yoredale 
series of Prof. Phillips, and in the limestone quarries in the neigh- 
bourhood of Richmond, but in none of these ]oc;alities have the 
spines of Ctenacanthus been discovered. Considering the large 
numbers of teeth of Cladodus which have been found, and the 
absence, hitherto, of any evidence of spines, even approaching in 
character to Ctenacanthus, negative evidence of considerable 
weight is afforded that the two genera were not so closely related 
as has been suggested, or at any rate, that the teeth of Cladodus 
may have belonged to a predaceous fish unprotected by fin-rays, 
in the Carboniferous area in this district. 
The genius Pristicladodus is in many respects similar to 
