MI ALL : BONES OF CTEXODUS. 
290 
mainly by evidence derived from the teeth, which are the only 
parts sufficiently numerous and sufficiently comparable with each 
other to yield serviceable characters. The collections now ac- 
cessible might seem at first sight copious enough to justify a con- 
fident opinion as to the number of species which they represent, 
but after some experience of the Rhaitic Ceratodus -teeth, I think 
a collection far larger than the largest yet made desirable, if not 
indispensable. Such a collection would pretty certainly con- 
tribute intermediate forms, and break down characters hitherto 
depended upon. Meanwhile I think it best to accept definitely 
only a small number of species, the most distinct being" apparently 
cristatus, obliquus and elegans. Others, either already named or 
hereafter to be proposed, will in time take rank with these, but we 
can well afford to wait till they are sufficiently investigated. The 
promulgation of new species based upon single examples of teeth 
is, as a rule, strongly to be deprecated. 
The student of Coal Measure Fishes will find that little of 
what has been written about Ctenodus need engage his serious 
attention. Agassiz' original description,* and Hancock & Atthey's 
valuable papers, f are of real interest and value. For comparison 
with Ceratodus, Dr. G anther's memoir^: and Prof. Huxley's shorter 
notice § are indispensable, while Dipterus may be studied in Hugh 
Miller,! Pander** and Traquair.f f Prof. Huxley's sketch of the 
classification of the Ganoid Fishes.Ji though in parts superseded 
by the increase of knowledge is now as formerly rich in hints and 
anticipations profitable to the inquirer. 
* Poissons Fossiles, torn. iii. 
+ Nat. Hist. Trans., Northumberland and Durham, vols. iii.. iv., ami v. 
(1868 — 76). See especially vol. iii., p. 54 ; vol. iv., pp. 397 and 417 : 
vol. v., p. 227, and the corresponding plates. These papers appear- 
ed also in the Annals of Natural History at about the same times. 
t Phil. Trans., vol. 161, pt. ii., p. 511. (1871). 
§ Proc. Zool. Soc. p. 24. (1876). 
*[[ Footprints of the Creator. 
** Ctenodipterinen des devonischen Systems. (1S5S;. 
tt Annals of Nat. Hist... 5th ser.. vol. ii., p. 1. (1878). 
XX Dec. Geol. Survey, pt. x. (1861). 
