1883.] 319 [Cope. 



First premolars only one-rooted ; canine small ; incisor very- 

 large Mixodectes.* 



aa. Last inferior premolar with internal tubercle. 



A very large ? canine ; first premolar only, one-rooted Microsyops.\ 



A very large ? canine ; first and second premolars both one- 

 rooted Cynodontomys.X 



The genera of Anaptomorphidse, which on dental characters includes 

 Indrodon, differ as follows : 



a : Incisors three. 

 First superior incisor without inner lobe ; posterior inner tu- 

 bercle present on first and second tubercle Indrodon. 



aa. Incisors two. 

 First superior incisor with inner lobe ; no posterior inner 



tubercle on superior molars Anaptomorphus. 



The superior dental formula of Indrodon is I. & ; C. £ ; P-m. £ ; M. ■#. 

 The canine is compressed and acute ; the third premolar is compressed 

 conic, and has two roots. The fourth premolar has but one external cusp. 

 The external cusps of the true molars are conic and acute, and are con- 

 nected with the internal cusp by ridges which form a V. Posterior inner 

 cusp distinct on ms. i and ii, a part of the posterior cingulum. Intermedi- 

 ate tubercles present, small. The superior incisors are well developed, 

 and display no tendency towards the rodent type. A portion of lower jaw 

 adheres to the skull, and may belong to the same animal. It supports 

 the last two molars. These have two anterior, opposite, approximated 

 cusps. The heel of the penultimate molar is rather large, and has a raised 

 edge, which develops low tubercles at the angles. 



Char. Specif. The first and third superior incisors are a little larger 

 than the second. Canine preceded and followed by diastemata, each of 

 which is 1.5 times as long as the long diameter of the base of the crown. 

 Premolars separated from each other and from the first true molar by in- 

 terspaces half as long as the diastema. Neither tooth has any basal 

 tubercles, but the posterior has a weak external cingulum, which is 

 stronger posteriorly. The internal cusp of the same tooth is anterior, is 

 acute and elevated. The superior true molars have a strong external 

 cingulum, which rises into a small tubercle opposite the space between the 

 external principal cusps. Of the latter, the anterior is a little more conic 

 than the posterior, and both are well within the external border. On the 

 last molar, the posterior external cusp is continuous with the external in- 

 termediate tubercle, and forms a cutting edge within the posterior margin 

 of the crown. The posterior inner tubercle is rather large, and projects 

 further inwards than the apex of the anterior V on the second true molar, 

 but not so far as in the species of Anisonchus and Haploconus. 



* Proceedings American Philosophical Society, 1883, p. 559. 

 fLeidy Report U. S. Geol. Survey, Terrs. I. 

 X Cope, Pal. Bull., No. 34. 



