78 Mr. T. Atthey on various Sjyecies q/'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 TristichojHerus being provisionally 

 associated with themt- 



There is nevertheless some doubt as to the propriety of 

 merging the genus Ctenodus in that of Dijyterus. In the early 

 part of this year (1867) I was fortunate enough to meet with 

 a small fisli in the shale at Newsham, which, though in a very 

 imperfect condition, exliibits 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 distm'bed state, seem to 

 differ considerably from those of Bipterus^ 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 pos- 

 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 tlie exposed portion tliere is a sort of 

 rosette which is defined posteriorly by incomplete concentric 

 wrinkles ; a few similar wrinkles or marks of growth extend 



* Trans. Geol. Soc. ser. 2. vol, iii. (1835). 



t Huxley, * Memoirs of the Geological Survey,' decade 10, p. 24. 



X Fred. M'Coy, ' Synopsis of British Palosozoic Fossils,' p. 591. 



