HAPLODONTIDA—SKULL OF HAPLODON RUFUS. 567 
dividing them seems to be constantly formed by a pair of plates not com- 
pletely fused; and, just in advance of the main foramina, there is a single 
median azygos foramen leading into the nasal cavity. This singular opening 
appears to be constant, and it is of notable size. The palate anterior to the 
intermolar portion has its sides rapidly sloping upward from the middle line, 
the actually flat and horizontal portion being extremely narrow, and bounded 
by a pair of ridges leading from the outer borders of the incisive foramen, 
with some sulcation between. The intermolar portion of the palate is per- 
fectly flat as well as horizontal, and also rectangular, the lines of the molar 
series being parallel; this portion equals in length the portion anterior to the 
molars, and reaches back of the molars for a distance equal to the width of a 
molar, ending behind with a simple concave edge. There are two pairs of 
small foramina respectively opposite the last and the penultimate molars, while 
behind and a little to the inner side of the last molar, on each side, is the 
larger palatine foramen proper. The portion of the palate anterior to the 
molars, that between the molars, and the post-palatal remainder of the base 
of the skull, are all of approximately equal lengths. The pterygoids are, 
unfortunately, defective in all the specimens before me; they appear, to judge 
by what is left of them, to have been simple laminz, probably hamulate or 
faleate, and approximately parallel with each other. The large foramina 
appear external to their ends, as in other Sciuromorphs. The interpterygoid 
space is directly continuous with the basioccipital, though with some down- 
ward trend. The basioccipital, in consequence of the approximation of the 
ends of the auditory bulla, rapidly narrows in front, having a general trian- 
gular shape, bounded behind by the condyles and paroccipital processes, on 
the sides by the bull, in front by the narrow basisphenoid ; its surface shows 
lateral paired depressions separated by a median lengthwise ridge. _ The audi- 
tory bulle are of large size, and horizontal as well as nearly transverse in 
position, their long axes being nearly coincident; in shape they are somewhat 
flask-like, being regularly hemispherical at base, then contracting beyond the 
swollen part, with a tubular prolongation, which extends outward to or some- 
times even beyond the extremity of the mastoids, and ends with a simple 
circular orifice of large calibre, with very thin walls. Their boundaries may 
be traced in the adult, which is the case with few of the bones of the skull. 
Behind the bulla appear the paroccipitals and mastoids. The glenoid fossze 
are of large size, especially long antero-posteriorly, broad and shallow, nearly 
