298 
MI ALL : BOXES OF CTENODUS. 
Bones of the Fins. A crushed bone, which may have been a 
humerus or femur, has occured, and a smaller but generally similar 
bone is also known. No specimen which I have seen is at once 
undoubtedly part of the skeleton of Ctenodus, and instructive as to 
the osteology of the animal, whether Ctenodus or some other,, to 
which it belonged. 
Fin-rays, probably assigned correctly to Ctenodus, have 
occured, but I am not acquainted with any feature of interest in 
a well authenticated example. If Dr. Traquair's identification of 
Campylopleuron with Ctenodus* is well founded, (and this I have 
no reason to doubt) we learn thereby that Ctenodus had a contin- 
uous diphycercal tail-fin, like Ceratodus, and unlike Dipterus, in 
which last-named genus dorsals and anals are differentiated. 
Some of the bones, like the teeth, of Ctenodus are divisible 
by their size into well-marked groups, which have some probable 
relation to at least as many distinct species. Thus three species 
are clearly indicated by the various parasphenoids known, 
and three by the opercula. Unfortunately, our opportunities of 
precise information are hitherto so few that we can rarely refer 
the bones to their species except in this rude way. Judging from 
occasional juxtaposition with teeth (the parts on which all the 
species at present recognized are based), and also from differences 
in the size of the bones corresponding to those which the teeth 
present, we should refer the fossil remains to three groups of 
species somewhat as follows : — 
Lakge. 0. cristatus., Ag. 
C. tuberculatus, II. & A. 
Medium. C. imbricatus, H. & A. 
C. obliquus, H. & A. 
C. ellipticus, II. & A. 
Small. C. elegans, H. & A. 
To what extent these and other species which have received 
names are distinct from each other is a question which I do not 
propose to discuss here. If decided in our time it must be decided 
* Nature, vol. xviii. ; p. 4S3. (1878). 
