7 2 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
nasals has been made a basis for specific distinction, Hegetotherium cunea- 
tum being founded on an individual in which a tongue of the frontals 
is produced between the nasals (text fig. 15, A), but as transitions maybe 
observed between this extreme and the normal in Hegetotherium mirabile 
(text fig. 15, B, C), it seems probable that these are merely individual 
Fig. 15. 
Hegetotherium mirabile , showing variation in the shape of the fronto-nasal suture, x f . A, No. 
9156 American Museum collection; B, No. 15,341 ; C, No. 15,542. 
variations. The interorbital tract is quite broad, plane in some individ- 
uals, slightly concave in others, and is perforated by one or more supra- 
orbital foramina. The interfrontal suture persists. The postorbital pro- 
cesses are large and bilobate. Their posterior borders are confluent with 
the slight temporal ridges, which converge far back on the parietal, giving 
rise to a low sagittal crest. The brain case is proportionately wider than 
in Protypotherium or Inter at her ium , but not as wide proportionately as in 
PacJiyrukhos. Numerous foramina perforate the parietal tract. The 
outer margin of the temporal fossa is sharply defined by the elevated 
border of the zygomatic process. This crest terminates a short distance 
anterior to the inion, from which it is separated by the mammilated sur- 
face of the squamosal, inclosing a deep groove continuous anteriorly with 
the temporal fossa. In Protypotherium and Inter at tier ium it is produced to 
the inion, joining the lambdoidal crest. In some individuals the inter- 
parietal suture remains distinct ; in others it is entirely obliterated. The 
suture between parietal and supraoccipital lies a short distance anterior 
to the lambdoidal crest, exposing a narrow tract of the supraoccipital in 
superior view (PI. I, fig. 2). 
On the back of the skull (PI. I, fig. 4; text fig. 14) the mastoid is 
