HAPLODONTID^B— SKULL OP HAPLODON PUFUS. 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 laminae, probably hamulate or 

 falcate, 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 bullae, rapidly narrows in front, having a general trian- 

 gular shape, bounded behind by the condyles and paroccipital processes, on 

 the sides by the bulla?, in front by the narrow basisphenoid ; its surface shows 

 lateral paired depressions separated by a median lengthwise ridge. The audi- 

 tory bulla? 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 fossa? 

 are of large size, especially long antero-posteriorly, broad and shallow, nearly 



