Il4 THE ENTOMOLOGIST. 



Let Yiiccae, therefore, be retained in Hesperidae. 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 Yuccse, 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 1 have little doubt that the last-named 

 yjlants will also be found to nourish other species of the 

 Tribe, 



Enemies. — I have reared from the yucca borer eleven 

 Tachnia flies, all belonging to the species which I have 

 designated anonyma, and which infests the larvae of a number 

 of other Lepidoptera. The fact that Yuccas 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 

 I'rom 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 tin)e 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, 



