STRUCTURE OF CERTAIN PALAEOZOIC DIPNOI. 
167 
The inner face of the roof-bones has a polished surface and usually bears 
radiating ridges. The outer face varies a good deal in surface character, but 
it is generally granulated, with a varying degree of gloss, and shows fine lines 
radiating on each bone from a central pit or rosette. Bundles of these lines 
often run from the rosette of one bone to that of the next. Rosettes are 
always more strongly developed on the frontal and squamosal than on the 
other bones. The whole appearance of the bones suggests that the head was 
Fio. 3. * 
Sagenodns. Nasal and prenasal bones. Q and R after Fritsch, all the rest from specimens 
in the Atthey Collection from Newsham, x about f . 
A-M, pvenasal ossicles : F, G, H, J, under surface, the rest dorsal aspect. 
N-S, nasals: P, under surface of 0; S, a remarkable form which would not fit into any 
skull yet seen. 
covered only by a thin skin^ and not, as in Ceratodus, by scales. This 
supposition is confirmed by the occasional appearance of the grooves of 
sensory canals on the skull-rooE. A well-marked lateral-Hue groove is 
seen to run from the rosette of the "parietal,"' first to the rosette of the 
