1004 The American Naturalist. [November, 
element which extends externally from the exoccipital to the quadrate 
is continuous with the opisthotic, but the semicircular canal is included 
in its proximal part only. Here the structure is entirely different from 
that which characterizes the Squamata, where the opisthotic does not 
extend distad of the canal and fuses early with the exoccipital. This 
character is to be added to those which distinguish the Rhynchocepha- 
lia from the Squamata. The paper which Dr. Baur criticizes above 
had reference to the Squamata, and the question at issue is what is the 
element attached to the end of the parotic process of the exoccipital in 
this order, which I call paroccipital, and which Dr. Baur calls squam- 
osal. That it is not the opisthotic is clear enough. 
The reasons for supposing that the element which I call paroccipital 
in the Squamata is really such, are as follows. In the orders 
Testudinata and Rhynchocephalia, where a continuous element extends 
from the posterior semicircular canal to the quadrate, this so-called par- 
occipital is not distinct. In the Squamata, where the opisthotic is re- 
stricted to the region of the canal and does not reach the quadrate, this 
so-called paroccipital is distinct. It becomes then probable that the 
paroccipital of the Squamata is represented by the distal, non auditory 
part of the element whose auditory portion is the opisthotic of the 
Testudinata and Rhynchocephalia. This hypothesis is confirmed by 
the structure in the Pythonomorpha, which is intermediate between 
that of the two types mentioned. The paroccipital extends proximad 
to the position of the opisthotic and petrosal, which it does not do in 
the Lacertilia or the Ophidia." 
Neither Owen nor Huxley distinguished the single element of the 
Testudinata as composed of two. The name paroccipital is the prior, 
and I have retained it for the distal or quadrate portion, while Hux- 
ley’s name of opisthotic belongs to the auditory portion for which he 
designed it. The direct evidence for such a primitive division of this 
element in the Testudinata has, however, yet to be produced, and I am 
entirely willing to give up the view above defended should it turn out 
on further investigation to be untenable. 
II. THE AFFINITIES or THE PYTHONOMORPHA. 
No one who has examined carefully the relations of the parocci- 
pital to the surrounding proximal elements in this suborder and com- 
pared them with their relations in the Lacertilia, can fail to see the 
important difference between the two. My opportunities of studying 
4 See Transac. Amer. Philos. Soc., 1892, p- 19, where the structure in Mosasau- 
rus is represented in fig. 3. 
