CONDYLARTHEA. " 409 



The inferior premolars have no internal cusp or crest, but the P-m. iii and 

 iv have a heel. The true molars have anterior and posterior intermediate 

 tubercles. The last true molar has a heel. The premolars in both jaws are 

 large. 



The difference between this genus and Periptyclms is well marked in 

 the superior true molars ; the two genera are otherwise much alike. The 

 inferior premolars of Anisonchus differ in the absence of the internal cusp. 



There are three ^ell-marked species of this genus, which differ as 

 follows: 



Internal lobes of superior premolars conical; width of base of second true molar, .010; 



large -I- coniferus. 



Internal lobes of third superior premolar conic; of fourth, flattened and concentric; 



width of M. ii, .007; length, .004; small A. gillianus. 



Internal lobes of the superior premolars flattened and continuous with ciugula; width 



of M. ii, .006; length, .0046; medium A. sectorius. 



The type, and first discovered species, is the A. sectorius, which is also 

 the most abundantly represented in my collection. 



Anisonchus coniferus Cope. 



American Natural iat, 1882, p. — (Sept. 28). 

 Plate XXIV 3; fig. 6. 



This is the largest species of the genus, and the largest of the Perip- 

 tychickB after the species of Periptychus. My knowledge of it is based on 

 fragments of two skulls which exhibit the superior molars following the 

 P-m. i, and the crowns of the inferior P-m. ii, and M. ii and iii. A calca- 

 neum of appropriate size accompanies the jaw-fragments. 



The second superior premolar is a robust tooth with a subtriangular 

 base, and simple conical external cusp, and a small internal basal cusp. A 

 trace of anterior, but no other cingulum. The third premolar is more 

 robust, and probably has a larger internal cusp, but this is worn off by 

 mastication. There are faint anterior and posterior ciugula not connected 

 with this cusp; none externally or internally. The fourth superior pre- 

 molar has a much greater transverse extent. Its external cusp is simple, 

 and without accessories, while the internal is large and is connected by its 

 edge with a well-marked anterior cingulum. A weak posterior cingulum; 

 none external. Crown worn. The true molars are distinguished by their 



