2.18 
ON TIIK STliUCTlTRE AND CLASSIFICATION 
Dentition — i 
DRYOLESTES, Marsh, 1 1878. 
The angle of the jaw is slightly intlected. The 
lower jaw is massive and has a rounded 
lower border and elevated incisor al- 
veolar border, as in the last genus. 
The condyle is concave transversely 
and slightly above the level of the 
teeth. The middle internal cusp of 
Fioukk 28. Lea lower jaw of Dryolesteg pmcua, inner molars is as high as or higher than 
view • three times natural size, a, canine ; a, symphysis. rpi . • 
AoTr’ Marsh. ^he Outer mam cone. The canine is 
bifanged. The incisors are sub-erect and expand at the tip. 
ASTHENODON, Marsh, ^ 1887. 
Dentition— I „ c,, pm„ m,. The median incisor is very large, the series being 
semi-procumbent and decreasing towards, the canine. The canine is rather small. 
A B 
Kiqubk 21>. a, right lower jaw of Aalhenodon aegnia, inner view; d, angle. B, anterior portion of same 
outer view ; tliria- times natural size, o, canine. After Marsh. 
The molars resemble those of Dn/olestes, but lack the third postero-internal cusp; 
they are more uniform in size behind the first premolar which is rudimentary. 
LAODON, Marsh,® 1887. 
Dentition — i f, c j, pm fj, m^. The molars in this genus have the outer main 
cone high and pointed, but the inner opposite 
cusps are greatly reduced in size. The canine 
is bifanged. The lower jaw is intermediate 
I'lUDKK 30. U'tt lower jaw of ikioiton cenu«tus, in form between Dryolestes and Stylacodon. 
M.r,h. inner view ; four times natural size. backwards 
and is not inflected. 
.INCERT./E SEDIS. 
Ihc genus I^ptocladus is isolated from the remainder of the jurassic group and 
yet is not sufficiently characteristic, or well known, to be placed in a distinct family. 
* Am. Joiirn. Sc. and Arts,” 1878, p. 459. These three genera are chiefly described from the figures and 
text of Professor Marsh’s article, and in part from his previous papers. It seems rather improbable that 
/O on had live prcmolars, as it would in such case form an exception to the entire sub-group. 
•'‘.\m. .lur. Mamm.,” pp. 3.36 and 337. 
••'Am. ,Tur. Mamm.,” pp. 336 and 337. 
