1898.] DR. BASHFOED DEAN ON PALjEOSPONDYLUS GUNNI. 347 



facial. Thus he himself rejects the most significant point of 

 comparison of Palceospondylus with cylostome. 



{b) To the second criticism, that in regard to the possible hetero- 

 cercy of Palaospondylus, there is needed but a brief explanation. 

 For in the first place Dr. Traquair, so far as I am aware, does not 

 use either term, diphycercy or heterocercy. His figures, however, 

 indicate clearly the diphycercal condition. I now remember, how- 

 ever, that I qualified it in parentheses as " perhaps heterocercal," 

 owing to the following sentence in Dr. Traquair's third paper ' : — 

 " A specimen which I obtained last autumn . . . shows that the?e 

 rods or spines (of the tail-fin) were considerably longer than they 

 had been represented in any of my figures, and consequently that 

 the fin was so much deeper " ^ : — does this mean heterocercal ? 



(o) That Dr. Traquair has mistaken my use of the terms radial 

 and hasal fin -supports is possibly due to a hasty reading of ray 

 paper. The questionable markings had been described as lying 

 within the line of the body-wall, therefore obviously interpretable 

 as basals. They are, however, of the narrow rod-shaped form 

 characteristic of radial fin-supports, and have, therefoi-e, been 

 termed from their shape " radial-ZiX-e." 



To return next to the question of the affinities of Palceospondiflus. 

 The structural evidence it presents in likeness and unlikeness to 

 the Marsipobranchs has already been tabulated, and may be repeated 

 with additions (see p. 346). 



Fi'om this comparison I am led to believe that Palceospiondylus 

 should not be given a place — even a provisional one — among the 

 Marsipobranchs, leaving out of question the possibility of its having 

 paired fins ^. The weight of evidence certainly falls on the unfavour- 

 able side. But what position can be assigned to so problematical a 

 vertebrate '? Dr. Traquair agrees that " if Palceospondylus be not 

 a Marsipobranch, it is quite impossible to refer it to any other 

 existing group of Vertebrata." Until at least a more definite 

 knowledge of its structures shall warrant the change, systematists 

 may be willing to accept it as the representative of the new sub- 

 class (or class ?) Cyclicn, constituted for it by Professor Gill *, 



Columbia University, 

 Feb. 7, 1898. 



^ Proc. Roy. Phys. Soc. Edinb. xii. p. 316. 



^ The italics and parentheses are mine. 



^ If the markings be the basalia of paired fins, the latter would certainly be 

 of a ptychopterygial form. The markings cannot well be neural and hfemal 

 spines, for reasons already given ; nor ribs, from their size or shape ; nor casts of 

 muscle-plates, first from their shape, and second from their position, for in the 

 neighbourhood of the gills muscle-plates, as experience has shown, are least 

 likely to be preserved 



* ' Science,' July 3, 189G. 



