VAEIOUS SPECIES OF CTENODUS. 55 



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 Ctenododipterini — Ceratodus and Tristi- 

 chopterus being provisionally associated with them.f 



There is, nevertheless, some doubt as to the propriety of merg- 

 ing the genus Ctenodus in that of Dipterus. In the early part of 

 this year (1867) we were fortunate enough to meet with a small 

 fish in the shale at Newsham, which, though in a very imperfect 

 condition, exhibited some features that perhaps should make ua 

 pause before we lay aside altogether the generic appellation Cte- 

 nodus. 



The specimen alluded to is proved to belong to this genus by 

 the presence of four dental plates (two palatal, two mandibular), 

 three of which are distinctly displayed in the crushed head, and 

 the fourth is inferentially recognisable. Now the scales of our 

 specimen, which are in a disturbed state, seem to differ consider- 

 ably from those of Dipterus, in which they are described to be 

 perfectly cycloidal ; that is, that they are circular and imbri- 

 cated4 In the Newsham species, which is named in the sequel 

 C. elegans, though they must be considered also of the cycloidal 

 type, yet they are not truly so, notwithstanding that they are im- 

 bricated. When detached they are seen to be parallelogrammatic 

 in form, with the posterior or exposed end well roimded, 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 an- 

 terior portion being much narrowed and truncated. They are 

 all thin and dehcate, but large for the size of the fish, and are 

 minutely grooved or plaited from end to end, the ridges being 



* "TrnTisactions Geological Society," Ser. 2, Vol. III. (183."j). 



t ■■ Ihixley, "Memoir.s of the Goolofiical Survey," Decade 10, p. 21. 



X Fred. M'Coy, "Synopsis of British I'aliuozoic Fossils," p. OiU. 



