192 
PROF. D. M. S. WATSON AND MR. E. L. GILL ON THE 
muscles. The species " Ctenodus interruptus" from the Lower Carboniferous, 
though proved by its cranial roof (fig. 23, B, p. 192) to be a true Ctenodus, 
has a palate and tooth-plates which in all respects much more nearly resemble 
those of a Sagenodus (see fig. 24, p. 193). 
The Quadrate. 
The bone which we take to be the quadrate of Ctenodus is represented in 
fig. 11, A and B, p. 177. There are two or three examples of it in the 
Atthey Collection, and one of them was labelled by Atthey himself " Ctenodus, 
OS quadratum." Fig. 11, p. 177, shows sufficiently how it differs from the 
quadrate of Sagenodus, the most striking difference being the much smaller 
development of the longitudinal ridge on the inner side. 
Fig. 23. 
Ctenodus. ■ 
A. Cranial roof of a specimen of C. ci-istatus from Lougton, Staffs. B.M.N. H. 7300. 
B. Cranial roof of " Ctenodus intemqytus, Bavkas," Dunnet shale, Straiton, Midlothian. 
1895/155/12, R.S.M. Of importance aa being the most perfect cranial roof of this 
species existing, and ."showing more connected circumorbitals than any other specimen 
of Ctenodus known. The detached circumorbitals are preserved on the counter slab, 
and really partially underlie those which are attached to the roof. A palatal tooth, 
omitted from the figure for the sake of clearness, establishes the specific identitj' of 
the specimen, x ^. 
The Loioer Jaw. 
Remains of the lower jaw of Ctenodus are scarce, but specimens from 
Newsham in the Atthey Collection and in the British Museum make it 
possible to reconstruct the jaw as has been done in fig. 27, p. 196. In 
general plan, and to a large extent in detail as well, it agrees with the jaws 
■of Sagenodus (fig. 12, p. 178) and Ceratodus (fig. 13, p. 179). The chief 
difference is in the greater breadth of the tooth-plates and, correlated with 
it, the greater width of the '' dentaries." Instead of coming almost or quite 
to a point in front, as do the "dentaries" of Sagenodus, those of Ctenodus 
have a wide anterior edge and carry the front ends of the angulais some 
