PETERSON : DESCRIPTION OF NEW RODENTS 183 
appears to be crowded especially posteriorly, where the tympanic bulla is encroach- 
ing upon it. The posterior part of the basisphenoid sends a backward projecting 
process on either side of the median line. These processes are fused with the internal 
face of the otic bulle, and extend to a considerable distance back on these bones. 
The pterygoid fossa is quite large, and the external wing of the pterygoid seems to 
have reached well back, and is fused with the floor of the brain-case very close to 
the antero-external face of the tympanic bulla. The foramina, ovale and rotundum, 
seem to be coalescent, as in Aplodontia. 
The Jugal is nearly vertical anteriorly, and is a comparatively heavy plate of bone. 
In shape and size it is very nearly like that of Castor, the vertical portion just back 
of the orbit being comparatively deeper than in the recent genus. At the extreme 
inferior jugo-maxillary suture, the arch forms a heavy, rounded, tubercle-like angle. 
At the supero-anterior portion the suture is not distinct, but I would judge that 
the jugal forms a suture with the lachrymal; the suture of the latter bone is also 
indistinct. ‘There is a Jarge lachrymal foramen in the orbit, similar to that of Castor. 
The greatest width of the skull is obtained across the posterior part of the jugal. 
The extraordinary width and strength of the zygomatic arch is one of the principal 
characters of the skull, and recalls such recent forms as the Geomyide and Aplo- 
dontia, and also the Loup Fork Mylagaulids. 
The postorbital process on the jugal is fairly well developed in Euhapsis platyceps. 
The orbit is imperfectly rounded, and is placed high. 
The Maxillary. — The zygomatic arch of the maxillary is very similar to that of 
Castor, but arises more posteriorly on the maxillary (opposite m+), than in the 
beaver (opposite p*). The infraorbital foramen is small and almost entirely hidden 
by a vertical ridge or projection from the maxillary like that in Castor. In fact the 
skull in this region resembles the recent beavers, with the exception of the much 
more produced angle at the inferior jugo-maxillary union on the zygomatic arch. ' 
The Premaxillaries. —'The premaxillaries are broad, short, and heavy. — Inferiorly 
the palatal surface is comparatively broad and has not the long, gentle, and concave 
antero-posterior sweep between the alveolar border of the maxillaries and the inci- 
sors, which is seen in Steneofiber fossor and the recent beavers. In this respect 
Euhapsis platyceps is more nearly like Arctomys monax, which has a continuous, 
almost horizontal palatal surface from the posterior nares to the incisors. The 
posterior limit of the premaxillaries in Huhapsis is just back of the long, narrow 
incisive foramina; thence the suture ascends in an almost vertical line immediately 
in front of the preorbital foramina to the superior borders of the zygomatic proc- 
esses, and across the face in a slight posterior obliquity to meet the posterior 
