148 J, He LEES 
nares particularly occupy very different positions. In the European 
form their anterior limits lie behind those of the preorbitals, while in 
Paleorhinus the whole of the nares lies considerably in advance of the 
preorbitals. 
The paroccipital processes are much wider in Mystriosuchus and 
cover the parietals. The posterior wings of the pterygoids are, how- 
ever, much smaller and shorter and leave a large opening which in 
Paleorhinus is filled by the quadrate and pterygoid. 
Some of the distinctions mentioned above as well as those indicated 
in the table of dimensions might be considered as being merely specific, 
but some are undoubtedly of generic rank. Such are the differences 
in dentition and relative major dimensions of the skull, in location of 
the nares, in the position of the parieto-squamosal arcade, and its 
relations to the supratemporal fossa. These divergences would seem 
to be amply sufficient to warrant the separation of the individuals into 
different genera, as has been done. 
It is impossible to make a close comparison of this specimen with 
Lucas’ genus Heterodontosuchus. ‘This latter was founded on the 
imperfect anterior portion of a lower mandible, while as before stated 
the only portion of the mandible of Paleorhinus which is available is 
the posterior part, well behind the symphysis. If one may judge 
from the upper jaw of Paleorhinus there must be some difference in 
the teeth of the two specimens, since Lucas stated that in Heterodon- 
tosuchus these are separated only by an extremely thin film of bone, 
while in Paleorhinus they are from one-eighth to one-fourth inch 
apart. There is evidence also that this is true in the lower jaw. 
There is no indication of the “‘deep narrow groove” which Lucas. 
speaks of as extending “along the side of the jaw.” Neither do the 
teeth seem to have been compressed antero-posteriorly as in Lucas’ 
genus. On the contrary the sockets are quite circular. 
On the other hand there are some features in which the two speci- 
mens show a close similarity. In both specimens the teeth are set 
very obliquely in a broad, shallow groove, and the two anterior ones, 
together with the extremity of the jaw, are enlarged. (In all other 
forms where known the end of the mandible is enlarged and pre- 
sumably is so in Paleorhinus. The enlargement of the upper jaw is 
very noticeable.) 
