4 
cave to the anterior extremity of the crest, which slopes upwards. The 
incisive alveolus, though not prominent as in the Lystricomorpha, is on the 
inner side of the base of the ramus in front, and the enamel-face of the 
incisor tooth is directed more inwards than downwards. Above the alveo- 
lar prominence, the inner face of the ramus is gently concave. The ante- 
rior origin of the coronoid process is opposite the posterior border of the 
second molar, 
Measurements. 
Length of inferior molar series..........-.. 0 ee sere 
Width of anterior face of inferior incisor. . 
PLEUROLICUS SULCIFRONS, gen. et sp. nov. 
Char. gen. Fam. Saccomy die. Superior molars rooted and short-crowned. 
The crowns with a lateral fissure bordered with an inflection of the enamel 
sheath, extending to their bases. In the superior molars this inflection is 
on the external side, and does not divide the crown, Superior incisors not 
grooved. 
This genus is curiously near to the existing Heteromys and Perognathus, 
the two genera of Saccomyide with rooted molars. The former differs in 
having the molars divided into two columns, each of which is sheathed in 
enamel, while Perognathus only differs so far as I am aware, in having the 
superior incisors grooved. ' 
Specif. Char. This species resembles those of the allied genus Hntop- 
tychus in many respects. The superciliary borders are thickened upwards, 
forming two ridges, which enclose a groove between them which is more 
pronounced than in the Hntoptychus cavifrons. The muzzle is plane above 
and considerably wider than the interorbital space. The base of the ma- 
lar is thin and oblique, and the foramen infraorbitale exterius is well in 
advance of the molar teeth and at the anterior part of the maxillary bone. 
A groove passes backwards from its inferior border, terminating in a small 
foramen which marks a point nearly half way to the first molar. Within 
this, another shallow groove bounds the more prominent median line. The 
palatal surface exhibits two shallow lateral grooves, which commence op- 
posite the posterior border of the first molar. 
The grinding surfaces of the molars are transverse ovals, only interrupted 
by the exterior fissure. The first molar is slightly different in form, being 
larger, and its section, when not much worn, being nearly round. Its an- 
terior portion extends towards the alveolus, giving an antero-posterior oval, 
on prolonged wear. Each tooth has three roots, one interior and two 
exterior ; in the first they may be described as two posterior and one ante- 
rior. The last molar is the smallest, the series exhibiting a regular grada- 
tion in size. ’ 
Measurements. : M. 
Interorbital width.............. Shc a Nees § sesthceasiees 0050 
Width 6f muizzléat. MIddIE. so. nes eee eee nes 0080 
