1883. ] 311 [Cope. 
levisanus, but is much larger. I give here a synopsis of the species of the 
genus, so that its affinities may be better understood. In general, the 
genus Triisodon is characterized by the rudimental character in the infe- 
rior molars of the anterior cusp. It is thus like Jctops, but differs in having 
the fourth premolar different from the true molars and like the premolars. 
From Mioclenus it difters in having the anterior and posterior cusps of the 
inferior molars unequal; the anterior forming together an elevated crest 
with two apices, while the posterior are low, and on the borders of a heel. 
I. Cusps of inferior molars compressed. 
Anterior cusp de) gala yA ceursent' arate aver tines orais van OWaharse ine tl TL. quivirensis. 
IL. Cusps of inferior molars not compressed. 
Anterior cusp very low ; 7. rusticus ; T. levisanus, and 7. 
Anterior cusp as high as other anterior cusps to which it is 
T. bats fat ° ee 
+ conidens and 1. hetlprinianus. 
assurgens. 
closely united. 
In dimensions the 7. rusticus is about equal to the 7. quivirensis, thus 
exceeding the other species excepting the 7. conidens. The interior ante- 
Tor cusp is nearly as elevated as the exterior, and is united with it nearly 
to the apex ; the anterior cusp is a tubercle which projects forwards from 
ite anterior base. The heel of the tooth is wide, and is rounded poste- 
riorly, and supports three tubercles, an external, a posterior and an inter- 
nal, all in contact with each other, On the second true molar the internal 
anterior tubercle presents a slightly projecting edge anteriorly and poste- 
riorly, which bounds a shallow vertical groove of the mass which repre- 
sents their united bodies. This is not apparent in the first. The enamel 
18 smooth, but the animal is rather old. 
Measurements. M. 
ANUOTOPOSTETIOL vs scvee ees soe van, SOLRB 
Diameters of m. i 4 transverse..........+.. HOR hg: 0068 
P (LI ELOME Wag cle WN oe .0068 
vertical 
UC aHeL VEG Vin codiO0RS 
( anteroposterior ..... ETRY, oR 01387 
Diameters of m, ii 4 transverse........-.5 wee OW 
( : POOTIV Nv. 4 007 
vertical on is 
Weateel eau ein idee LOOCR: 
D. Baldwin, discoverer. 
TRiisopon ASSURGENS, 8p. Nov. 
This is the least species of the genus, and resembles in its inferior denti- 
tion the species of Diacodon. It is very much larger than the D. alticuspis, 
the larger species of that genus, which is found in the Wasatch formation, 
The 7. assurgens is known from a mandibular ramus which supports the 
last four molars, the last premolar having lost its principal cusp. The 
peculiarity of the true molars is seen in their generally more produced 
character ; the anterior cusps are higher and the heels are longer. The an. 
terior cusp is very small and basal; the principal anterior cusps are united 
