OK THE GENUS CTENOBUS. 103 



T. P. Barkas, and, I believ.e, Mr. Attliey also possess perfect speci- 

 mens in their cabinets. The tooth was imperfectly described by 

 Professor Agassiz in his " Poissons Possiles," but tolerably 

 figured. Professor Owen referred to the genus in his " Odon- 

 topography" among the Cestracionts ; and, if I mistake not, for 

 I have not the book at hand for reference, the tooth he figures, 

 and figures well, is one of C crisfatus ; but his remarks on the 

 external characters are too brief to be called a description, while 

 liis sketch of the minute structure is quite inaccurate. Messrs. 

 Hancock and Atthey, in a paper entitled " Notes on various 

 species of Ctenodus obtained from the Northumberland Coal 

 Pields," which appeared in the third volume of the "Transactions 

 of the Northumberland and Durham Natural History Society," 

 w^ere the first palaeontologists to give a complete description, and 

 it may be summed up as follows : — Tooth plate-like ; rather thin ; 

 irregularly elliptical ; inclining to ovate ; 2t inches long, li inch 

 broad (these measurements are, of course, average) ; the upper 

 surface somewhat hollowed or concave ; inner margin well arched, 

 the outer much less so ; upper surface is covered with twelve 

 close-set transverse ridges, which are studded from end to end 

 with closely arranged tubercles ; ridges increase in size externally 

 and incline towards the anterior and posterior margins, thus 

 appearing to radiate ; grooves angulated ; tubercles perfect only 

 on outer margin and are covered with brilliant enamel ; base of 

 each tubercle subtriangular ; the imperfect tubercles are 

 much worn and compressed laterally ; tubercles and ridges 

 coarsely and irregularly granular. Mr. T. P. Barkas, E.G-.S., 

 briefly describes his specimec, in a paper on " Ctenodus," which 

 appeared in the " Greological Magazine " for July, 1869. 



G. Bohertsoni is only referred to by Agassiz himself in the 

 " Poissons Possiles" ; he neither describes its external character 

 nor does he figure them ; but he refers slightly to its micro- 

 scopical characters, and attempted to pourtray them ; the 

 description and engraving are, however, nearly valueless from 

 the meagreness of the one and the low power of the microscope 

 that has been employed in examining the other. 



C. MurcMsoni was named by Agassiz, but neither described 

 nor figured by him ; and Pictet merely gives the name and 

 founder of the species in the second volume of his " Traite de 

 Palseontologie." 



C. alah(s, from the Old Bed Sandstone, is merely mentioned by 

 name by its first observer, Agassiz, in his " Poissons Fossiles." 



C asteriscus (Agassiz), also from the Old Bed Sandstone, is 

 just hinted at by name by Giebel in his " Fauna der Yorwclt." 



The four last-mentioned species may or may not be true species 

 for anything I know to the contrary ; and I am not aware that 

 any palaeontologist who is acquainted with the recent discoveries 



