11 



and merging into the chitinoiis membrane surrounding the plate; as 

 these are of excellent taxonomic value we refer to them later under the 

 name "Lateral fold." The lateral portions of the posterior margin 

 are drawn out into chitinous processes of varied length and shape 

 which extend backward beyond the vaginal orifice, often for a con- 

 siderable length and which we have termed "Alae." 



The PosTVAGiNAL PLATE is 3. small chitinous area, situated pos- 

 terior to the vaginal opening and not connected, except by the gen- 

 eral surrounding membrane, with the vaginal plate proper. Its pos- 

 terior margin is usually considerably hollowed out and the whole area 

 is finely spiculate; it offers nothing of any particular taxonomic value. 



As regards the geographical distribution of the family it is, as 

 far as our present knowledge goes, confined to the southern portion 

 of the United States, to Mexico and to Central America. One spe- 

 cies (yuccac) extends northward along the Atlantic seaboard into S. 

 Carolina; two forms (yuccae coloradcnsis and streckeri) have been 

 captured in S. W. Colorado ; Wright records nenmoegeni from the 

 eastern borders of Southern California. The most southerly species 

 is indecisa which Druce records from Costa Rica and Panama ; the 

 dry arid regions of Mexico, Texas, New Mexico, and Arizona where 

 the Yuccas and Agaves flourish seem to be the principal home of the 

 race. The relative scarcity of specimens in collections at the present 

 time is due, we imagine, less to the actual rarity of the insects than 

 to the fact that very little collecting has been done in these barren and 

 desert tracts of country. 



Concerning the imaginal habits we know very little. Blasquez 

 observes that hcspcriaris is diurnal in its flight, but emerges from the 

 pupa at night. The flight is in August and September and there is but 

 one brood yearly. Riley states that the flight of yuccae is diurnal, and 

 that "during the months of April and May, in South Carolina, but 

 earlier in more southern latitudes, the parent Megathymus may be 

 observed, where the Yuccas abound, passing, with very rapid, darting 

 flight, from plant to plant, remaining but a few seconds at one place, 

 during which she fastens an egg to some portion of a leaf. She is 

 generally seen at work in the morning hours." He also states that 

 there is but one generation annually. The neumoegeni group appears 

 also to consist of day-fliers, judging by Ottolengui's note (Ent. News 

 VI, 218). Their time of appearance is, however, in September and 

 October as far as we can tell from dated material before us. We have 



