SAUROCEPHALUS AND ITS ALLIES. 93 
The lower jaw of Suwrocephalus, as mdicated in the specimen of S. Leanus, preserves 
much more the form and general appearance of that of Sphyrena than the upper one. 
The dental bone has nearly the same outline of form as in the latter, but it is deeper in 
relation with its length, and is less convex externally. Its symphysis presents very much 
the appearance of that of Sphyrcena, though I am not satisfied that the comparatively 
feeble tubercle antero-internal to the dental border supported a large tooth as in this genus, 
and of which I can detect no trace. The articular bone holds the same relative position . 
as in Sphyrcena, as does also its articular process, which is however much more vertical 
in its direction. (Fig. 14.) 
The dental border of the lower jaw appears to have supported about forty-two teeth, 
which have nearly the same size and form as those of the upper jaw, in which respect 
this genus further strikingly differs from Sphyrena. The inner side of the dental border 
with its notches presents the same appearance as in the upper jaw. 
The more uniform size of the teeth in both jaws of Sawrocephalus approaches the genus 
more closely to another extinct allied genus, Sphyrenodus, than to Sphyrena, and indeed 
I have a suspicion that a careful comparison of the specimens upon which the two former 
genera were founded may prove them to be identical. 
Professor Agassiz has described and represented a number of isolated teeth (Pois. Fos. 
V. 102, pl. 25, ¢. figs. 21—29,) of a large sphyreenoid fish, from the chalk of Lewes, Eng- 
land, which he erroneously refers to the Sawrocephalus lanciformis, Harlan. Although 
teeth of the size of those in the fragment of an upper jaw, described by Dr. Harlan, might 
be inferred from the examination of the Sphyrena barricuda, to be accompanied with 
teeth in the lower jaw, as large as those attributed to S. lanciformis by Agassiz, yet the 
jaws of Saurocephalus Leanus, prove this not to be the case. 
The crowns of the teeth of S. lanciformis, Harlan, are almost as broad as they are long, 
and do not measure more than 23 lines, whereas the corresponding portions of the teeth 
referred by Agassiz to this species, as represented in his figures, measure from 5 to 15 
lines long, and from 23 to 6 lines broad. 
Dixon, in his Geology of Sussex, following Agassiz, refers portions of the lower jaw 
and teeth of a large sphyrenoid fish (pl. xxx. fig. 21; xxxi. figs. 12; xxxiv. fig. 11,) ap- 
parently the same as that indicated by the figures of Agassiz above noticed, also errone- 
ously to the Saurocephalus lanciformis. In a note to page 375 of the same work, he fur- 
ther attributes the rostrum of a Xiphioid fish (pl. xxxii.* figs. 1) to 8. lanciformis, to which 
it certainly does not belong. 
Professor Owen’s sectional view of the structure of the teeth of Sawrocephalus (Odonto- 
