STRUCTURE OF CERTAIN PALAEOZOIC DIPNOI. 175 
Fig. 11, C and D, p. 177, show good examples from the Low Main shale, 
Newshani, in the Atthey Collection. Both ends o£ the bone were expanded, 
the lower more so than the upper. One side oi: the shaft bore a pronounced 
longitudinal ridge or wing, better preserved in Williston's and some of 
Fritsch's examples than in ours. The aspect shown in fig. 11, C, p. 177, 
we take to be the inside of a right quadrate, and we suggest that the facet 
on the toe of the pterygoid was applied to the prominence there shown at the 
lower end of the bone on the right, possibly also engaging with part of the 
longitudinal wing. 
We have been unable to identify any further bones as belonging to the 
skull proper. Vomerine teeth w ei'e described and figured by Atthey (1877), 
and we see no reason to doubt his identification ; but n^o trace of bone is 
attached to these teeth, and it is probable that the vomers were represented 
solely by the bases of the teeth, as in Ceratodus. 
We have not been able, either, to identify any of the hyoid bones with 
certainty. Many large rib-like bones occur on slabs of shale among the 
other remains of Sagenodus, and there can be little doubt that some of them 
are hyoids, others probably cranial ribs. Fritsch was confident that he had 
identified both ; the bone he named " first cranial rib " (1889, Taf. 77, fig. 5) 
may well be such, but some of his " hyoids," especially that figured at 
Taf. 71, fig. 5, are probably not bones of Sagenodus at all *. 
Tlie Lower Jaw. 
The main features of the structure of the lovver jaw were made out many 
years ago. Hancock and Atthey described and figured the " splenial" in 
1872 ; and in 1877 Atthey announced the discovery of the angular 
(" articular "), which he had been able to identify by comparison with the 
newly-discovered Ceratodus forsteri. To complete the resemblance of the 
jaw to that of Ceratodus, a " dentary " f element was needed, and its 
existence in Sagenodus was first demonstrated by Watson and Day (1916), 
who found it in the form of a broken cross-section fitting on to the 
fiont of the angulars in a head in the Manchester Museum (L. 10904). 
In the Atthey Collection we have found an abundance of examples of the 
bone itself, some lying among the other remains of crushed heads and 
many others freed from the matrix. In the Dinning Collection, also in 
* Fritsch believed (p. 67) that he could recognize the bones of '•' Ctenodus obKqmis " with 
certainty by their lusti'e and coloui, and in a few instances this criterion possibly led him 
astray. 
t As will appear from a later discussion of tlie jaw of Dipterus, there is good ground 
for thinking that the bones here referred to as " splenial " and " dentary ' are not properly 
so named. But since, following Huxley (P. Z. S. 1876, p. 34), the corresponding bones in 
Ceratodus have long been known by those names, we retain them in this description, only 
placing them in quotation-marks. 
LINN. JOURN. ZOOLOGY, VOL. XXXV. 12 
