340 TRANS. ST. LOUIS ACAD. SCIENCE. 



CONCLUSION. 



Whether we have in our Yucca Borer a remnant of more, an- 

 cient 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 Hespe- 

 rians, 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 gieatest development in Central America and Brazil. The 

 few Castnioides known, inhabit the southern part of N. America. 

 During the tertiary period, when the ocean reached over the whole 

 Mexican plateau norihward, the fauna of North and South Ame- 

 rica 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 continent, 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, and 

 particularly to create genera, from mere drawings. Megathy- 

 mus, as founded on Boisduval's figures, is very much of a myth. 

 It is so with all genera erected by the mere coining of a name 

 without recognizable definition ; and while a Hiibner, in making 

 a number of divisions on superficial grounds, may accidentally 

 hit upon relationships which subsequent research proves correct, 

 he certainly does not greatly benefit science by his work. Again, 

 we may learn the necessity for the adoption by entomologists of 

 some rules for guidance in matters that do not come within the 

 scope of present accepted rules. Can names connected solely 

 with published figures be accepted? Shall we write Tuccce 

 Boisduval ox^Tuccce Walker? Such questions become the more 

 important when two dift'erent names are employed. A figure, 

 however good, cannot be considered a definition ; and, whilst 

 most entomologists would consider that the species in question 



* These Transactions, p. 203; 6th Mo. Ent. Rep., p. 150. 



