en opens onto the lateral surface of the maxilla. The opening is
the entrance to a canal that runs posteriorly above the tooth-row
throughout the length of each specimen. Beneath the naris the maxilla
extends as a broad tapering shelf, the ventral surface of which
articulates with the premaxilla. The narial rim is wide, but wider
ventrally than dorsally. The plane of the narial rim is oblique to the
lateral surface of the maxilla. The external surface of each fragment is
grooved and pitted. The ossification of each fragment appears to have
been complete.

TABLE 1.--DIMENSIONS, IN MILLIMETERS, OF THREE MAXILLARY FRAGMENTS OF
DELORHYNCHUS PRISCUS

Key:

A. Anterior height of fragment
B. Posterior height of fragment
C. Length of fragment at tooth-row
D. Dorsal length of fragment
E. Mean length of teeth
F. Anterior width of naris

============================================================
CATALOGUE NUMBER | A. | B. | C. | D. | E. | F.
AND MEAN | | | | | |
-----------------+------+------+------+------+------+------
KU 11117 | 6.0 | 8.0 | 6.0 | 8.0 | 3.0 | 3.0
KU 11118 | 6.0 | 6.0 | 9.0 | 8.0 | 2.0 | 3.0
KU 11119 | 6.6 | 8.0 | 10.0 | 11.0 | ? | 4.6
-----------------+------+------+------+------+------+------
Mean | 6.2 | 7.3 | 8.3 | 9.0 | 2.5 | 4.5
-----------------+------+------+------+------+------+------

_Discussion._--The Nitosauridae are small primitive edaphosaurs with a
moderately elongate face, sharp subisodont teeth, little development of
canines and few specializations. The jaw is of a primitive type and
articulates on a level with the tooth-row. The palatal dentition is
primitive (Romer, 1956:280). The nitosaurids are thought to be related
to the later Caseidae, and the most obvious structural similarities are
found in the postcranial skeleton (Vaughn, 1958:989). Cranial
resemblances between the families are fewer, but nevertheless indicate
that a nitosaurid-caseid relationship exists.

Vaughn (1958) described a small pelycosaur, _Colobomycter pholeter_
(Eothyrididae, Ophiacodontia) that structurally resembles the Caseidae.
This individual also was obtained from the Fort Sill locality. In
Vaughn's opinion the features of _Colobomycter_ indicate a close
relationship between eothyridids and caseids and the possibility that
the caseids may well have been of eothyridid rather than nitosaurid
derivation.