5 
W. B. Scott—Marsupial from the Colorado Miocene. 443 
prise that a far larger number of very small mammals should 
be found there than in the coarser matrix of the White River 
~ district in Dakota. 
Morphologically this new species is of very small value, as it 
throws no important light upon questions of descent. But as 
a contribution to geographical zoology it is of great interest. 
It demonstrates the fact that the small insectivorous opossums, 
now characteristic of South America, existed in Miocene times 
in North America, and is additional evidence that the latter 
continent is the source from which the former received the 
greater part of its animal population, just as the great Pale- 
arctic continent seems to have been the original source of the 
modern faunas of the Ethiopian and Oriental regions. us, 
the tapir, the llama tribe, many edentates, the peccaries, and in 
all probability the monkeys and cats, have been traced to their 
origin in North America.. The smal! opossum just described 
gives another characteristic feature of the South American 
fauna; and I may add that a small lizard from Chalk Bluffs, 
now in the Princeton Museum and as yet undescribed, points 
in the same direction. 
MEASUREMENTS. 
Length of molat series. ¢-2-..- 74. -.--25 0-007 
s Po eee ee 0-005 
sé “ec ev ee eas 0'002 
es bs a ie tao kee eee Goan 0°002 
" Site ea a ee 00015 
Height of €th molar. 220 ue oo gs 0-002 
Depth of ramus beneath Ist molar- --- ---- 0°0035 
Depth of ramus beneath 4th molar ------- 0°004 
For the accompanying sketch, as well as for the exceedingly 
delicate and difficult work of preparing and mounting this 
minute specimen, I am indebted to Curator B. C. Hill. ) 
Princeton, N. J., May 5, 1884. 
Am, Jour, Sc1.—Tarrp Szrrms, Vou. XXVII, No, 162.—June, 1884, 
30 
