1893.] On the Genera of the Dipnoi Dipneumones. 921 
to be desired when examined for the solution of the problems 
of to-day. 
Schneider's paper was based upon original investigation of 
a considerable number of African mud-fish from several 
widely-separated localities, and his conclusions are that Protop- 
terus is not only generically distinct from Lepidosiren, but that 
there are also two well-defined species of the African form, to 
be separated on account of the number of ribs, the presence or 
absence of the cartilaginous fin-rays and some other characters 
of no importance here. Baur’s paper is an historical resumé 
of the main facts about Lepidosiren paradoxa. In general, how- 
ever, the reasons which have been given for keeping Protop- 
terus distinct from Lepidosiren may be concisely stated as fol- 
lows: 
1. The presence of 4 gill-holes in Lepidosiren and 5 in Pro- 
topterus. 
2. The presence of a larger number of ribs in Lepidosiren. 
3. The absence of fin-rays in Lepidosiren and their presence 
in Protopterus. 
4. The absence of external gills in Lepidosiren and their 
presence in Protopterus. 
I shall now endeavor to show that the critics of my sugges- 
tion of the generic identity of these two forms have failed to 
bring any proof that it is not entirely reasonable and highly 
probable, and by their own investigation have weakened their 
case by discovering facts which go to prove the close relation- 
ship of these animals. 
THE GILLS. 
All the writers on this subject have failed to see the import- 
ant agreement between the gill structures of Lepidosiren and 
Protopterus, and have been led off to base important conclu- 
sions on a relatively unimportant point in their anatomy. The 
statement which Schneider and Baur base so much upon, viz. : 
that Protopterus has 5 gill-slits, while Lepidosiren has only 4, 
certainly looks important enough to give the advocates of a 
