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 cbaracter in the infe- 

 rior molars of the anterior cusp. It is thus like Mops, but differs in having 

 the fourth premolar different from the true molars and like the premolars. 

 From Mioclmnus it differs 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 very low T. quivirensis. 



II. Cusps of inferior molars not compressed. 



Anterior cusp very low ; T. rusticus ; T. levisanus, and T. assurgem. 

 Anterior cusp as high as other anterior cusps to which it is closely united. 

 T. conidens and T. heilprinianus. 



In dimensions the T. rusticus is about equal to the T. quivirensis, thus 

 exceeding the other species excepting the T. conidens. The interior ante- 

 rior 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 

 its 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 

 is smooth, but the animal is rather old. 



Measurements. M. 



C anteroposterior 0123 



Diameters of m. i < transverse 0068 



vertical < 



fin front 0068 



at heel 0038 



-I Li cxiia v fi sc . . • ....•••••.•■• . vvj i 



( <.. i f anteriorly 007 



^vertical < . J _„_ 



C anteroposterior 0137 



J ■ 



Diameters of m. ii ■< transverse 007 



f anteriorly 007 



I at heel 0062 



D. Baldwin, discoverer. 

 Triisodon assurgens, sp. 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 T. 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 



