' “Am. Jour. Sc. and .\rts,” 1881, p. 512. 
* “ Am. Jur. Mamm.,” p. 339. 
• “ Meoozoic Mammalia,” p. 41. 
2;{2 
ON THK STIiUCrrUKE AND (.CLASSIFICATION 
'interri-posterior faces of the upper and lower molars are deeply excavated and 
grooved. 'I'he second premolar is smaller than the first. Tlie premolars have dis- 
“ tinct external cingula. 
DOCODdN, Marsh,* * 1881. 
Dentition. — i 3, c j, pm 4, ni 7. This 
genus is closely similar to the prece- 
ding, but lacks the eighth molar. 
ENNEODON, Marsh,* 1887. 
Fkii'kk 22. Uigiit lower jaw of Diplocynodon victor, 
outer view, twice natural si/e. Dentition i C j, pm 3, m 3. The 
canine is very large. The surface of the premolars is grooved or striate. The 
antero-external cusps of the molars are less distinct than in Diploetjnodon. The 
second premolar is apparently missing. 
PERAMUS, Owen,* 1871. 
Dentititm — i c 7, pm and m 7. This genus may be provisionally embraced in the 
Ampldtheriidm as aboije defined. In En- 
neodon we observe that the antero-exter- 
nal cusps of the molars are slightly rotated 
inwards upon the inner face of the crown, 
as in Peramim (see Marsh, “ Am. Jur. 
Mamm.,” Plate X, fig. 2 , m3). The arti- 
Fiochk 23.— iiinht lower jaw of Docodon utriatiis ; cular portion of the jaw in Perannis is es- 
inner view, twice natural 8l/e. After Marsh. sentially similar to that in DildoetpiOilon, 
although the coronoid is slightly narrower. The condyle has the same level. The 
angle in Ixith is short and obtuse. 
'fhe formula assigned to Peramns, pm6,m7, upon page 202 of this memoir, was in 
view of the fact that only the three posterior 
molars possess antero-external cusps. But 
the presence of six premolars is so excep- 
tional a feature that it is probable that 
when seen upon the internal face (the outer 
face only is known at present) the formula 
would resolve itself into pm7 mj^. As thus 
divided, the jiremolars appear to lack posterior basal cusps, and have no external 
cingulum ; wlule upon the above hypothetical formula the anterior molars have no 
antero-external cusps. The main molar cusps are ‘ erect, and there is an anterior 
