114 THE ENTOMOLOGIST. 
Let Yuccw, therefore, be retained in Hesperide. By its 
aberrant characters it may constitute the type of a third tribe, 
for which I would propose the name Castnioides. This Tribe 
consists at present, in addition to Megathymus Yucce, of two 
other good species, the one from Mexico, the other from Costa 
Rica. It is very probable that this number will be greatly 
increased as we come more familiar with the Lepidopterous 
fauna of Mexico and Central America, where the yuccas and 
agaves abound; for I have little doubt that the last-named 
plants will also be found to nourish other species of the 
Tribe. 
Enemies.—1 have reared from the yucca borer eleven 
Tachnia flies, all belonging to the species which I have 
~ designated anonyma, and which infests the larve of a number 
of other Lepidoptera. The fact that Yucce is attacked by 
such a parasite is further proof that it is more or less an 
external feeder, since it is hardly probable that the parent 
Tachina would enter the burrow, and I know of no genuine 
endophytes that are similarly attacked. 
Conclusion.— Whether we have in our yucca borer a 
remnant of more ancient and synthetic types from which the 
Castnians on the one hand and the Hesperians on the other 
are derived, or whether we have in it a more recent variation 
from the more typical Hesperians, are questions which, with 
_ present knowledge, permit only of a speculative answer. The 
former hypothesis is, however, the more plausible. The 
Castnians, while occurring in Mexico, find their greatest 
development in Central America and Brazil. The few Cast- 
nioides known, inhabit the southern part of N. America. 
During the tertiary period, when the ocean reached over the 
whole Mexican plateau northward, the fauna of North and 
South America was much more similar than at the present 
time. It is not difficult to conceive how a Lepidopterous 
family that was then common to both divisions of the con- 
tinent, may since that time have deviated in the two directions 
indicated, and yet have left some less modified forms in the 
intermediate country. We are assisted in this conception if 
we view, with some botanists, the Yuccas as remnants of an 
ancient flora. 
We may learn from the history of this butterfly, as from 
that of the Hackberry butterflies, how unsafe it is to describe, 
