60  Ayress Description of a New Genus of Fishes. 
the tympanal. It commences by a thin edge near the inferior 
extremity of the jugal, grows broader, and again diminishes 
in such a manner as to leave between it and the jugal a small 
space at their superior portion. Into this space is inserted the 
wedge-formed extremity of another bone, which is without 
doubt the temporal. This passes upward and forward, and is 
apparently articulated upon the mastoid. A better idea, how- 
ever, of the position and form of these bones may be obtained 
from an examination of the figure than from description. It 
may be mentioned that the lines of division are given in the . 
figure with more distinctness than they occur in the speci- 
men. The osseous fibres of one part are so interlaced with 
those of the one adjoining that it is not easy to tell the pre- 
cise limits of each bone, though it is believed they are repre- 
sented with some approach to accuracy. 
It will be noticed that a triangular space remains between 
these bones and the upper jaw. Within this we should of 
course expect to find the other bones of the cheek, but instead 
of this, we have no sign of either ossification or apparent out- 
line of the position of a bone. Beneath the eye there is, it 
is true, a smooth, oval spot, about three-eighths of an inch in 
length, which seems to indicate a suborbital, though without 
any trace of bony matter, but this is all. 
The only part of the head not already mentioned, which is 
even imperfectly ossified, is the anterior portion of the roof of 
the mouth, a small space representing probably the vomer and 
perhaps part of the sphenoid. 
The opercular pieces we do not find, unless they are deno- 
ted by a membranous projection, which borders posteriorly 
the slender bone, supposed to be jugal, &c. This membrane 
commences at the upper extremity of the bone, and extends 
within about three-fourths of an inch of its lower extremity, 
where it terminates quite abruptly. Its breadth, which is 
pretty nearly uniform, was when fresh a little more than @ 
fourth of an inch. It exhibits some tokens of concentric 
structure. About three-eighths of an inch above its lowest 
