12 Dr. R. H. Traquair on the 



or subordinal importance is so close as, in my estimation, most 

 fully to justify the step taken eight years ago by Dr. Giin- 

 ther in associating the two genera in one common group 

 (Dipnoi), in which they respectively represent the two dis- 

 tiwct families of Ctenoclodi])terini and Sireiioidei. In retaining 

 the Dipnoi as a distinct order of fishes I shall continue to 

 follow Prof. Huxley ; the discussion of this question is beyond 

 the scope of the present paper. 



II. Paljedaphus, Van Beueden and De Koninck, and 

 HOLODUS, Pander. 



In 1864 a remarkable fossil from a Belgian Palaeozoic 

 limestone, formerly supposed to be of Carboniferous age, but 

 now, as I understand from Prof. De Koninck, referred to the 

 Devonian formation, was described and figured by the distin- 

 guished palgeontologist just named, in conjunction with Prof. 

 Van Beneden, and received from them the name of Palceda- 

 2jhus insignis'^. 



The Edinburgh Museum having recently, through the kind- 

 ness of Prof. De Koninck, acquired a plaster cast of the speci- 

 men, I have represented it much reduced in Plate III. figs. 5, 

 6, and 7. It consists of two rami closely united in front and 

 broken oif behind, the left one almost immediately behind the 

 union, the right somewhat further back. The aspect of the 

 fossil shown in fig. 6, considered by its describers to be the 

 upper surface of a head, is characterized by them as being 

 *' d'une apparence ecailleuse et brillante, comme si elle avait 

 ^te recouverte d'une peau corn^e, mais la couclie de mati^re 

 qui lui communique ce brillant est extreraement mince et assez 

 dure." The other aspect (shown in fig. 5) displays two large 

 dental plates, touching each other in the middle line for some 

 distance in front, and furnished each with four well-marked 

 rounded ridges passing from behind forwards in a slightly 

 radiating manner, there being also a slight appearance of cre- 

 nulation of these ridges, as seen in the profile view fig. 7. 

 In front of these dental plates, and separated from them by a 

 groove, the anterior margin, gently curved in contour, and 

 thick and rounded, seems formed as if by a folding-over of the 

 opposite surface ; on each side the outer extremity of this lip- 

 like margin is abruptly truncated, and presents an excava- 

 tion [y) bounded above, in front, and below by elevated 

 margins, butposteriorly passing uninterruptedly into a shallow 

 groove which proceeds backwards for some distance along the 

 outer aspect of the fossil (fig. 7). 



* BuU. Ac. Be:^. (2) xvii. 1864, pp. 143-151. The same fossil is also 

 figured in Gervais's ' Zoologie et Paleontologie fran^aises/ pi. lixvii. 

 fig. 17. 



