128 ILLINOIS BIOLOGICAL MONOGRAPHS [128 



Family Megathymidae 



No species of this small family is found east of the Rocky Mountains 

 and even there the boring habit of the larvae makes their discovery 

 difficult. Three specimens of Megathymus yuccae have been examined 

 and the following characters are taken from them. 



Head rounded, about as high as wide, rugose, partially retractile, 

 smaller than prothorax ; front triangular, sides almost straight, reach- 

 ing about half way to top of head ; labrum with a small, acute, mesal 

 notch ; setae very much reduced ; ocelli small, inconspicuous. Protho- 

 racic shield narrow, sometimes indistinct; setae of body much reduced, 

 apparently wanting on its dorsal half, numerous and short on ventral 

 half of first two thoracic segments, rare or absent on abdomen, except 

 on prolegs. Thoracic legs well developed, bearing numerous setae on 

 their caudomesal surfaces; prolegs short, bearing a complete ellipse of 

 biordinal crochets, series sometimes slightly broken at mesal and lateral 

 ends ; spiracles large, those of segment 8 placed somewhat farther dor- 

 sad than the others. 



Family Lycaenidae 



Head from one-sixth to one-half as wide as body, usually deeply 

 retractile, often overhung by the prothorax; front broad, often extend- 

 ing over half way to vertical triangle ; labrum various. Body depressed, 

 widest above prolegs, usually tapering strongly toward the ends; sec- 

 ondary setae numerous, sometimes in tufts and pencils, usually coarse 

 and short. This form of body does not occur elsewhere in Lepidoptera 

 except in the Zygaenoidea. Prolegs with a mesoseries of triordinal cro- 

 chets well developed at the ends of the series, shorter or interrupted at 

 the middle, and with a spatulate or clavate fleshy lobe arising near the 

 interruption (Fig. 79). 



From the very meager material at hand, the following synopsis 

 has been prepared. It follows to some extent that of Scudder : 



a. Head at least one-third the diameter of the body, 

 b. Head about one-half the diameter of the body. 



c. Verrucae large and distinct, with short setae. Eumaeus 



cc. Verrucae inconspicuous or absent, setae long, arranged in trans- 

 verse groups. Feniseca 

 bb. Head about one-third the diameter of the body, 

 c. Lateral line continuous and rather conspicuous. 



d. Prothorax longer and higher than mesothorax; abdomen 

 marked by a pair of subdorsal lines between mediodorsal and 

 lateral lines. Mitoura 



