THE STRrCTUEE OF CERTAIN PALEOZOIC DIPNOI. 3 63 
The Structure of Certain Paleozoic Dipnoi. By D. M. S. Watson, F.R.S., 
and E. L. Gill, M.Sc. (Communicated by Prof. E. S. Goodrich, 
F.R.S., Sec.L.S.) 
(With 34 Text-figures.) 
[Read 30th November, 1922.] 
This work began by an attempt to write an account of the structure of the 
Ooal-Measure fish Sagenodus and Ctenodvs on the basis of the splendid 
material in Newcastle. This collection when worked over by us left certain 
problems unsolved which have in part been cleared up by fossils in Edinburgh 
and elsewhere. During our search for this information we saw the splendid 
specimens of Uronemus in Edinburgh, and the wish for further light on 
certain morphological problems led us to extend the investigation to several 
other palaeozoic Dipnoi. 
The resulting paper now gives an account of the structure of these fish, 
which certainly includes the chief variants known to have occurred in the 
group, although some forms which might prove of great interest are still 
known to us only by the original descriptions or by unsatisfactory specimens. 
With the possible exception of Dipterus, the most completely known of 
the fossil Dipnoi is now Sagenodus, and we therefore deal with that fish first, 
following on with an account of the related genus Ctenodus. For these two 
genera, the chief source of our material has been the Atthey Collection in the 
Hancock Museum at Newcastle-on-Tyne, but additional information of great 
importance has been derived from fine specimens in the Royal Scottish 
Museum and British Museum (Natural History). 
The material is from the following horizons and localities : — 
Lower Carboniferous (Oil Shale group) : Broxburn, Loanhead, and 
other localities near Edinburgh — [Sagenodus and Ctenodus). 
Upper Carboniferous (Westphalian) : Newsham, Northumberland; 
Lougton, Staffs. ; Ardwick, Lanes. ; Newarthill, Lanarkshire ; 
Linton, Ohio ; Kansas — [Sagenodus and Ctenodus). 
Upper Carboniferous (Stephanian) : Nyran, Bohemia — [Sageno- 
dus). 
Lower Permian (Artinskian) : Wichita, Texas ; Kounova, Bohemia — 
[Sagenodus). 
Sagenodus, Owen. 
Until the publication of Dr. Smith Woodward's second volume of the 
" Catalogue of Fossil Fishes" in 1891, the generic distinctness of Sagenodus 
from Ctenodus was not generally recognized. Nearly all the published work 
of any importance on the structure of these fishes appeared before that date, 
