O. C. Marsh—Jurassic Mammals. 513 
Some of the dimensions of the type specimen are as follows: 
Distance from apex of canine to end of condyle. 31°™™ 
Extent of premolar and molar series --._------- hh 
Depth of lower jaw below last molar -...-----. 4 
Depth of lower jaw below eanine si. ics ee 
Haight of crown of catine -. 22. 6.655 soos ees 2°5 
The only known remains of the species are from the 
Upper Jurassic deposits in Wyomi 
Dryolestes gracilis, sp. nov. 
The present species, which is the smallest of the genus, is 
represented by several lower jaws, which are unusually long 
and slender, and nearly straight.. In the type specimen, there 
d 
‘were eleven teeth behind the canine, which was of moderate 
Ny 
size. The fangs of the molar teeth are not placed one in 
front of the other, but opposite, teas one large fang on the 
outside, and a small inner one beside it. ‘This peculiar feature 
appears in all the species of qpean ee: but has not been 
observed in other mammals, recent or extinct. Th 
pylohioe groove in this specimen is , and extends 
forward, neonly parallel with the lower border, to the sym- 
pe depart he following measurements show the size of the 
est preserved lower jaw referred to the present species : 
Extent of eleven mses {60th . 6.2 sect acweiss 1 Soup 
Extent of last five t ni iti ck ae eecateuns, 6° 
Depth of jaw below canine .--.-.-...-.-.----- - 
Depth of jaw below fect. pape Pec utie pete bees 2° 
All the known specimens of this species are from the Upper 
Jurassic deposits of Wyoming Territory. 
Yale College, New Haven, May 24th, 1881. 
