2 
and .S. pansus. The posterior fossettes of the crowns seen in those species 
are wanting in the 4. gradatus. 
ENTOPTYCHUS CAVIFRONS, gen. et sp. nov. 
Char. gen. Probably of the family Suscomyide.* The cranium is 
elongate, and presents inflated periotic hones, and slender zygoma. The 
foramen infraorbitale is small and anterior in position, entering the maxil- 
lary bone near its suture with the premaxillary. 
Generic characters. Molars +-4, rootless, and identical in structure. The 
crowns are prismatic, and in the young stage present a deep inflection of 
enamel from one side, the external in the superior teeth, the internal in the 
inferior. After a little attrition, the connection with the external enamel 
layer disappears, and there remains a median transverse fossette, entirely 
enclosed by enamel. The tooth then consists of two dentinal columns in 
one cylinder of enamel, separated by a transverse enamel-bordered tube. 
Incisors not sulcate. 
The teeth of this genus differ from those of Perognathus in being with- 
out distinct roots, and in having the enamel loop cut off and enclosed. In 
Dipodomys, the molars are uudivided simple prisms. 
Specif. Char. This species is represented by some entire crania, and 
numerous separated jaws. The postorbital part of the skull is subquadrate 
in outline, and depressed in form. The interorbital region is narrowed, 
but the superciliary margins dy not meet. nor converge to form a sagittal 
crest. They are thickened, forming two subparallel ridges which are sepa- 
rated by a shallow concavity of the frontal hone. The nasal bones are very 
narrow, and their posterior apices just ultain the line of the supero-anterior 
angle of the orbit. The base of the malar bone is much elevated and very 
oblique. The molar teeth are directed obliquely backwards, the alveolus 
of the first issuing below the anterior part of the orbit. The first superior 
molar is the largest, and the proportions of the others diminish regularly 
posteriorly. The first inferior molar is a little smaller than the second and 
third, and is about equal to the fourth. Its anterior column is contracted, 
while the last molar is like the second and third. The face of the inferior 
incisor is flat, and its enamel is smooth. The external face of the jaw is 
bounded below by a strong angle, as far anteriorly as below the first molar. 
Measurements. M. 
Length of skull to incisive alveoli..............---006. 041 
Width of skull at mastoids...............--...0-00 020 8- -020 
es ef DEEWCEH-OFDItS noc neuiee cia a wakwe Bite oe -005 
ne “© at middleof muzzle: ccc cd aaeccwse -010 
Elevation of skull from second molar.................. O11 
Length of molar seriesi ss sccvscssvecronss gedvotarcues 007 
© first Molar cc+ ccsesecoveweeeeseees Geee yes -002 
Width of <“ UE tale Aoitacd SiS PRR Naeeeut o Nee ee aneutiere ty aan waters 002 
Length of crown of last molar.............-.e eee eens 0015 
*see Coues’ Report U.S. Geol. Surv. Terrs. XI, p. 491- 
