78 Mr. T. Atthey on various Species of Ctenodus 
and described similar palatal plates attached to the roof of the 
mouth of a small fish belonging to the Old Red Sandstone, 
which had previously been described under the generic appel- 
lation of Dipterus by Sedgwick and Murchison*, thus at once 
removing Ctenodus from among the Sharks and Rays, and 
placing it in the order Ganoidei. Since that time Ctenodus 
and Dipterus have been considered synonymous, and have 
recently been transferred to a distinct family named Ctenodo- 
dipterini— Ceratodus and Tristichopterus being provisionally 
associated with them f. 7 
There is nevertheless some doubt as to the propriety of 
merging the genus Ctenodus in that of Dipterus. In the early 
part of this year (1867) I was fortunate enough to meet with 
a small fish in the shale at Newsham, which, though in a very 
uaperaees condition, exhibits some features that perhaps should 
make us pause before we lay aside altogether the generic 
appellation Ctenodus. 
The specimen alluded to is proved to belong to this genus 
by the presence of four dental plates (two palatal, two mandi- 
bular), three of which are distinctly displayed in the crushed 
head, and the fourth is inferentially recognizable. Now the 
scales of our specimen, which are in a disturbed state, seem to 
differ considerably from those of Dipterus, in which they are 
described to be perfectly cycloidal—that is, that they are cir- 
cular and imbricated{. In the Newsham species, which is 
named in the sequel C. elegans, though they must be con- 
sidered also of the cycloidal type, yet they are not truly so, 
notwithstanding that they are imbricated. When detached, 
they are seen to be parallelogrammatic in form, with the ane 
terior or exposed end well rounded, the anterior only slightly 
arched; the sides are nearly parallel, being a little inclined 
inwards or hollowed; in length they are nearly twice their 
breadth. Some few, however, differ very much from the above 
description, being shaped like a battledore. These have the 
posterior half greatly enlarged and rounded, the anterior por- 
tion being much narrowed and truncated. ‘They are all thin 
and delicate, but large for the size of the fish, and are minutely 
grooved or plaited from end to end, the ridges being very finely 
denticulated and curved towards the centre of the rounded ex- 
tremity, where they become confused and irregularly nodose. 
Thus in the centre of the exposed portion there is a sort of 
rosette which is defined posteriorly by incomplete concentric 
wrinkles ; a few similat wrinkles or marks of growth extend 
* Trans. Geol. Soc. ser. 2. vol. iii. 1835). 
t Be ne ‘Memoirs of the Geological Survey,’ decade 10, P 24. 
t Fred. M‘Coy, ‘Synopsis of British Paleozoic Fossils,’ p. 591 
