18 
outwards, and follows closely the maxillary bone well posteriorly. It then 
turns inwards, extending to the parasphenoid bone, with the wide portion 
of which it has an extensive contact. It then turns outwards as pterygoid 
bone, and rapidly narrowing, joins the inner distal extremity of the quad- 
rate. It thus encloses a foramen with the quadratojugal bone, which is 
much smaller than the choanodrbital foramen. The posterior part of the 
inferior surface of the bones of this arch, not including the slender ptery- 
goid portion, is roughened with hard nodules resembling teeth in material, 
and serving the purpose of such organs. 
Two rod-like bones extend outwards and backwards frem the posterior 
part of the parasphenoid and the basioccipital, which belong to the inferior 
arches. The anterior is the larger, and is bent backwards at an obtuse 
angle ; its proximal extremity is a truncate oval. This bone occupies the 
position of the stapes. The second is extensively in contact with the basi- 
occipital by its proximal extremity. It is curved backwards at its distal 
third. The occipital condyle is represented by a fish-like cotylus, which 
has a deep notch at its superior border. : 
The mandible has a short angular process, vertical by lateral compres- 
sion. The symphysis is very short and the Meckelian cavity large, and 
completely enclosed. 
The anterior cervical vertebre consist of the same elements as the dorsals. 
The intercentra of the second and third vertebrae support capitular costal 
articulations, somewhat elevated above the surrounding level. ne pleuro- 
centra do not support the ribs, but the neural arches terminate below in 
diapophyses. There isa pleurocentrum in front of the second intercentrum, 
and above and in front of ita neurapophysis, which has no distinct diapoph- 
ysis. Its superior portion is a subacute process which is not in contact 
with that of the other side, but is separated from it by a vertical osseous 
plate, which is probably the neural spine of the second vertebra or axis. 
This is similar to the structure already observed in Hryops, and the parts 
being in place, should explain those of that genus. The portion of the 
atlas which represents the intercentrum is divided into two lateral portions, 
each of which has the form of an entire intercentrum, i.e., crescentic. . 
The intercentrum of a cervical of a large species of this group, is wider 
than that of the other vertebre, and presents two articular facets anteriorly. 
Specific Characters.—The skull is flat and rather wide, the length ex- 
ceeding a little the transverse posterior diameter. The posterior borders 
of the orbits mark a point half way between the extremity of the muzzle, 
and the posterior supraoccipital border. The orbits themselves are of 
medium size, and are separated by a space about equal to their transverse 
diameter. Their form is a wide oval, with the long axis obliquely antero- 
posterior. The diameter of the external nostril is nearly half that of the 
’ orbit, and the form is similar to that of the latter. The interorbital and 
ethmoid regions are concave ; the prefrontal regions are convex. The su- 
praoccipital border is strongly concave; and the notch separating the 
cpiotic angle from the quadrate angle is as deep as the supraoccipital. Tue 
