86 Bulletin American Museum of Natural History. [Vol. XXXIV, 
This genus is characteristic of the Torrejon, where it is represented by 
two species, D. navajovius Cope and saurognathus Wortman. A third species, 
D. europeus, is recorded from the Cernaysien of France. A small species 
from the Wasatch was referred to the genus by Osborn and Wortman in 
1892, but Matthew in 1909 separated it as a distinct genus Hapalodectes. 
True Dissacus does, however, appear to be represented by three specimens 
from the northern Wasatch, one from the Clark Fork, two from the Gray 
Bull beds. The first represents an undescribed species, the others I cannot 
separate by any specific distinctions from D. navajovius of the Torrejon. 
The European species, Plesidissacus europeus Lemoine, was refigured by 
Boule in 1903 and referred to Cope’s genus. The type is part of a lower jaw 
with Ds-Me, and agrees with D. navajovius in size and such characters as can 
be observed in the figure. It is retained as a distinct species upon Boule’s 
authority. 
Key to Species of Dissacus. 
A. Larger species with robust molars, massive jaw, powerful canines and heavy 
jaw condyles. Limbs robust, feet spreading, pollex complete. 
1. Mis = 57 mm.; paraconids large on ps-m2; m; smaller than m2; ms; with 
small paraconid and reduced heel................... D. saurognathus. 
B. Smaller species with more compressed molars, canines and jaw condyles smaller 
and jaw more slender. Limbs slender, feet compressed. 
2. My3 = 33 mm., paraconids small on all teeth; m, smaller than mg, heel of ms 
Os ees a eons D. navajovius. 
3. Mis = 38 mm., paraconids somewhat larger, m, as large as me, heel of m; 
BPOCUCCU th a ee es yo a D. navajovius longevus. 
4. Molars intermediate in size between D. navajovius and saurognathus, para- 
conids more reduced than in either, metacone of ms, vestigial. 
D. prenuntius. 
Dissacus navajovius longevus mut. nov. 
Type, 15732, a lower jaw with ps—ms, from the Gray Bull beds of Shoshone River 
in the Big Horn Basin. 
Distinctive characters: Mi_3 = 38 mm., m; as large as ms, m3 smaller with reduced 
heel, paraconids larger than in D. NAVAJOVIUS. 
The type consists of a nearly complete left ramus. A second specimen, 
No. 15229, comprises parts of the lower jaws of a young individual with milk 
premolars and mi». On account of the individual variation among speci- 
mens from the Torrejon referred to D. navajovius, I regard this as represent- 
ing rather a progressive mutant than a distinct species. Although the 
metaconid is not more reduced than in the Torrejon specimens, the propor- 
tions of the molars and size of the paraconid constitute an approach towards 
Pachyena. 
