MI ALL : BONES OF CTENODUS. 
of the palato-pterygoid of Dipterus into lateral halves, which was 
supposed to constitute a difference between Dipterus and Ctenodus, 
is due to fracture, and has no anatomical or zoological significance. 
The ossification of the hinder end of the bone is more complete in 
Ctenodus than in Ceratodus, and it bears what looks like a wide 
trochlear surface in some well-preserved examples of the former 
genus, as if it had entered into the articulation of the mandible, 
investing and replacing the cartilage of the suspensorium to an 
unexpected extent. That such was really the case, and that the 
palato-pteiygoid formed, or even entered into the joint of the 
mandible, I think highly improbable, but I have as yet seen no 
quadrate bone nor any cavity for the cartilaginous suspensorium. 
Probably the posterior end of the palato-pterygoid curved round 
the edge of the palato-quadrate cartilage. In Dipterus, as Dr. 
Traquair shows, there is a bony quadrate, apparently distinct 
from the contiguous bones, and the skull is autostylic. There is 
nothing to show that this was not also the case with Ctenodus also. 
Parasphenoid. Both upper and under surfaces are figured. 
Fig, '6.- Cilnodus Parasphenoid. A. upper surface. B, under surface, x \. 
