Cope.] 316 [Dec 7, 
These species differ as follows : 
I. Posterior cingulum of true molars i and ii, wide, rising into a small 
cusp. 
Length of trie molare, Ma OUGG is i ieis cb Wile bee eho eo OV aserColLeaene, 
If. Posterior cingulum distinct, thickened inwards. 
Length of true molars (m. ii inferential) .0175, crowns narrowed, trans- 
VEUEC ues svn wol awe dare vows ease Mim ay Wce elyicds Ctlad'y ete wR OMMCCIUVEsUCCE ay 
Length of true molars .0170; crowns quadrate..............8subtrigonus.* 
Length of true molars .0135 ; crowns narrowed, transVerse.....sseesvers 
(Chriacus) simplen. 
III. Posterior cingulum weak, disappearing inwards. 
Length of true molars .0105, crowns transverse except the third, which is 
VOUY SMALL. sec vi ve eWec tie vwedeselbever vas tay) uiblean ves we  MMEQUIGENS, 
Char. Specif. The Tricentes crassicollidens is about the size of the 
Chriacus truncatus and resembles it a good deal. The latter has, however, 
a more transverse form of true molars, as compared with the present spe- 
cies, where the form is subquadrate. In the present animal the premolars 
are smaller, and if the third (second present) has an internal cusp, it is 
much more ins:gnificant than in the C. truncatus. ‘These two species and 
the Mioclenus opisthacus resemble each other in the similar size, and in the 
true molars having the posterior inner cusp more distinct than in other spe- 
cies. They differ in the dimensions of their premolars, those of the If 
opisthacus being the largest, and those of CO. truncatus being intermediate 
in size. In the 7. erassicollidens the anterior cingulum is also distinct. The 
external cusps are conic, and are well separated, and the internal V is dis- 
tinct. The internal cusp of the fourth premolar is small and compressed, 
so as to be transverse. The base of the third premolar is triangular and 
much longer than wide, All the superior molars, except the first premo- 
lar, are furnished with an external cingulum, which rises into a more or 
less distinct apex at its anterior and posterior angles. The first’ premolar 
isa simple cone. The alveolus of the canine tooth is of large size. The 
last true molar is not much reduced, and the first is as large as the second. 
This is not the case with the 7. buceulentus, where the first is considerably 
smaller than the second. 
Measurements. M. 
Length of dental series to canine, exclusive............ .086 
ig MT AUELCMID ys vos vud veld b viet anes n ee tines 4l om 6 eee el OUR 
®y TT OROMLOLT RELIONV 6 ebrtreuuvaveeeener ihe seven sivOLEO 
o CV MOUO MOM BOMB) Caves vib vb ors eet esionbie eve deals SOLOS 
SANUETOMOBLGTION rises iceveevenee «OUMS 
Diameter of P-m. iv 
Wa varme ss CP EE he goals 
*There may be two species confounded under this name, A specimen figured 
in Vol, III of the final (4to) Report of the Hayden Survey, Plate XXIV, f, fig. 4, 
has four interior premolars, all simple, 
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