
774 THE AMERICAN NATURALIST.  [Vor. XXXVI. 
New York he inspected some of the material obtained by 
Professor Newberry for the museum of Columbia University. 
He regarded * Cladodus " as a shark which had become highly 
specialized and adapted to bottom living. Against this view 
it is merely necessary to note that Cladoselache possessed 
dorsal fins, one of which was situated well forward on the 
trunk region, its anterior rim lying above the pectoral fin, a 
condition entirely unknown in any depressed type; that the 
caudal fin was of a peculiar form, extreme in its heterocercy, 
and provided on either side with broad, stout lateral flanges 
closely comparable to those of such swift-swimming forms as 
Isurus, or even scombroid fishes. It is evident that none of 
these characters can be associated with a bottom-living form 
such, for example, as Rhina. Moreover, if Cladoselache were a 
bottom-living form, its fins would obviously have been larger in 
proportion to the size of the animal than those of recent sharks. 
In this connection, however, it is only just to Dr. Jaekel to 
State that at the time of his visit to Columbia University none 
of the best material of this form had yet been obtained, — that 
the caudal and dorsal fins, for example, were not known. 
A second writer, Professor Semon, in one of his studies on 
Ceratodus (Forschungsreisen, Bd. I (1898), pp. 105—106), sub- 
scribes to a page of general denial as to the primitive nature of 
Cladoselache. As he does not, however, refer to the detailed 
literature upon this form, quoting only from a single and semi- 
popular article, and in view of other omissions, I am inclined to 
believe that his criticism is inadequate. Thus I note that he is 
unaware that the horizon of Cladoselache is now conceded 
(cf. Orton and others) to be Upper Devonian instead of Lower 
Carboniferous, and that he puts this form in the Coal Measures 
side by side with xenacanthids, whose structural characters are 
known only from the Permian ; also that he states that dipnoans 
(he does not mean by “dipnoans,” I take it, the very problematical 
arthrodires, since these are naturally included in the term“ placo- 
derm," which he specifically mentions) and crossopterygians were 
already present in Silurian times,— a statement I can only account 
for on the basis either that he has collected data which, when 
published, will throw light upon this empty page of the geological 
