STRUCTURE OF (JERTAIN PALEOZOIC DIPNOI. 
189 
llie Roof of the Skull. 
The skull of Ctenodus was ossified to the same extent as that o£ Sagenodus, 
and similarly shows no trace of ossification of the neural chondrocranium. 
A comparison of fio-. 1, p. 164, and fig. 21, below, will show that the skull- 
roofs of the two genera differ considerabl}' — more, in fact, than any other 
Fig. 21. 
p.na. 
Ctenodus oibtattis. Cranial loof. /?'., fiontal; «./;•,, mtei frontal; i.m« , intemasal, item, 
intertemporal; mn?-., marginal bones ; par., "parietal" (= parietal + dermo-supra- 
occipital) ; p.fr., pre- or post-frontal; p.na., prenasal; .fq., "squamosal''; tab., 
"tabular" (=tabular-f- supratemporal). X about -5. 
