Dr. R. H. Traquair—Devonian Fishes of Canada. 263 
re-examining the specimens already in the Museum, I find that there 
is no doubt whatever, that in all of them the dorsal fin is in two 
distinct portions, which are separated from each other by a very 
perceptible interval. 
The anterior dorsal commences far forwards; it is low and 
fringing in character and the length of its base is contained two-and- 
a-half times in that of the posterior dorsal, the interval between the 
two fins being equal to one-third of the length of the base of the 
anterior. The base of the second dorsal extends to a point a little 
beyond the commencement of the lower lobe of the caudal, but as its 
rays are long, and the posterior ones directed nearly horizontally 
backwards, the fin seems to extend near to the tip of the tail. It 
_ does not, however, form a continuous dorso-caudal as in Phanero- 
pleuron, as hitherto described, or in Ceratodus or Uronemus, and Mr. 
Whiteaves is certainly in error in making it do so in his restored 
ficure already referred to. As regards the caudal fin it is in reality 
heterocercal, the upper lobe being represented only by very short 
rays towards the tip of the body prolongation, while on the ventral 
aspect the lower lobe is of the triangular form characteristic of 
Dipterus. Indeed, the resemblance of the fins to those of D. 
macropterus, 'Traq., from John O’Groat’s, is very remarkable, the most 
striking difference being the more extended base and fringing form 
of the anterior dorsal in the species under consideration. Dipterus 
Valenciennesii, D. macropterus and Scaumenacia curta form then a 
complete and most interesting series as regards the configuration of 
their dorsal fins; in the first both dorsals are short based, in the 
second the posterior dorsal has a base of considerable length, in the 
third the anterior dorsal is long based, while the base of the posterior 
one is still longer than in the second. 
The question here arises,—what is the condition of the dorsal fin- 
arrangement in the typical Phaneropleuron Andersoni, Huxley ?—for 
on that depends the validity of the new genus which I propose, 
provisionally at least, to institute for the reception of Whiteaves’s 
Ph. curtum. In the Dura Den fish the dorsal fin was originally 
described by Huxley, and afterwards by myself, as continuous 
anteriorly, and if that description holds good Ph. Andersoni occupies 
the fourth place! in the series of dorsal fin differentiations, and the 
Canadian species is also generically distinct. The specimens of Ph. 
Andersoni in Edinburgh or even in the splendid collection of Dura 
Den fishes at St. Andrew’s are not sufficiently perfect in the region 
to afford a decided answer, and I regret that since this question came 
under my notice, I have not had the opportunity of re-examining 
those in the London collections, though here it must be noted that 
Mr. Smith Woodward, in his catalogue of the Fossil Fishes in the 
British Museum, pt. ii., p. 247, states that the dorsal fin of Phanero- 
pleuron is ‘‘single,” and it certainly appears to be so represented in 
Huxley’s figure of the finest specimen of Ph. Andersoni in that 
Museum. I feel therefore justified in provisionally erecting the 
1 As a matter of evolution the series would of course be reversed, Phanero- 
pleuron being first and Dipterus Valenciennesii last. 
