376 The Extinct Rodentia of North America, {April 
mandibular rami are completely coossified. They are united at 
their lower borders poste- 
rior to the divergence of 
their dental ridges, by the 
expansion of the stout mb 
of their inner face which 
encloses the’ incisive alve- 
olus. 
The dental formula is 
1.1; Co: My i 
cisors have a moderately 
thick enamel layer whichis 
wrapped round the exter 
nal angle a short distance 
Their sculpture is not deep 
ly cut. The molars a 
composed of vertical col- 
umns of dentine enclosed 
in and separated by lamine 
of enamel. The columm 
are more or less transvers, 
and are neither confluent 
nor divided in any of ' 
teeth. They number a 
ior teeth, excePr 
the superior t mer 
n 
thin 
Fic. 27.—Jaws of Amblyrhiza latidens Cope, 
two-thirds nat, size, from Anguilla, W. I. Orig- 
ig. a, superior incisors from above; enamel plates are 
on the 
di Jengi 
‘ddle of their leth 
be middle at 
4, lateral view; Fig. c, inferior inci fi 
helow; d, do. hve aa, Woh aari o rected backwards ja 
grinding faces. The extremities of the roots are simple ere) p 
tracted to an obtuse termination. The inferior molars ; 
their form, being straight and directed obliquely pi? es ast 
the jaw. From this it results that their triturating SY rior 0 
oblique to the axis of the teeth, while those of the sup®° 
