122 Proceedings of the Royal Physical Society. 
confluent, short conical teeth.1. Such an important difference 
in dentition seemed to me in 1890 amply to justify the 
separation of Uronemus from Phaneropleuron and its allies 
in a distinct family of Uronemide.? 
Mr Smith Woodward, however, in the second part of his 
“Catalogue of the Fossil Fishes in the British Museum,” 
retains the family of Phaneropleuride, in which he also 
still includes Uronemus. That Uronenvus must, on account 
of its non-ctenodont dentition, be placed in a different 
family from Phaneroplewron, is, as I have above stated, 
perfectly clear to my mind at least; for the rest, the Phanero- 
pleuride are separated from the Ctenodontidz, according 
to Mr Woodward’s definition, by the possession of marginal 
teeth and of jugular plates. As regards the former character, 
I believe it to be founded on a mistaken interpretation; as 
to the latter, are we quite sure that we know the structure 
of Ctenodus sufficiently well to be able to decide with cer- 
tainty as to whether it had jugular plates or not ? 
Mr Woodward also erects a separate family for Dipterus, 
that of the Dipteride, the essential characters of which, as 
distinguished from those of the Phaneropleuride, are,—the 
absence of marginal teeth, and the hecterocercal configura- 
tion of the tail; this form of caudal fin, along with the 
possession of jugular plates, distinguishing it from the 
Ctenodontide. It is not necessary to repeat what has 
been said as to the marginal tooth question; as regards 
the heterocercal tail in opposition to the diphycercal form, 
if we accepted that as a family character in the Crossop- 
terygian fishes we should separate genera which otherwise 
are most closely allied. Take the Rhizodontide, for example 
—in Rhizodopsis the tail is heterocercal, in Gyroptychius as 
nearly as possible diphycercal; so in like manner the most 
marked distinction between Tristichopterus and Husthen- 
opteron is the decided heterocercy of the former and the 
nearly perfect diphycercy of the latter. But the median 
fin-system of Scawmenacia is connected by so perfect a 
transition through Dipterus macropterus to that of the typical 
1 Geol. Mag. (2), vol. ix., p. 543. 
2 Proc. Roy. Soc. Edin., vol. xvii., p. 393. 
