DEPARTMENT OF THE INTERIOR
UNITED STATES GEOLOGICAL SURVEY

Cambridge, June 23, 1891

My dear Marsh,

Will you be good enough to give me a clue to the time of
the appearance of the Bovidae and Cervidae in this country, or tell
me where I can learn the details regarding them? The reason I ask
is that I have just found among the Florissant fossils a remarkable
genus of bot-fly, a family which, while it attacks to some extent
almost all the terrestrial Mammalia, yet confines its attention
now-a-days very largely to these two families. I suppose these
families did not appear until Miocene times, whereas this fly is
from the Oligocene. Of course it could have attacked plenty of
the other families, especially among the Artiodactyla, but consid-
ering what an annoyance the Oestridae are, it is a little curious
that these ruminants should have attained such a predominance in
the world despite the fact that these flies were awaiting their ad-
vant; if it be a fact, which is what I want to know. Answer me at
your leisure.

Dictated.