15 



stroke; in hcspcriaris (PI. Ill, Fig. 3) this specialization is not pres- 

 ent ; it evidently represents a more primitive form, approaching in 

 this respect the Hespcriidac; in all the other members of the family 

 this peculiar structure is present, but with a different degree of in- 

 tensity. In the nciimocgcni group (PI. Ill, Fig. 5) it is not well 

 marked, vein Cuj being only slightly bent towards CU2, in yuccae 

 (PI. Ill, Fig. 13) and sniithi it is more pronounced, and in streckeri 

 (PI. Ill, fig. 4) we find the culmination of the specialization, veins 

 Cuj and Cuj being very closely approached and both arising from 

 close to the base of the wing. 



In the form and vestiture of the palpi we have apparently a means 

 of differentiation between the two genera; at least in an examination 

 of all the species known to us we have been able to find no intergrading 

 forms between hcspcriaris on the one hand (genus Acgiale) and the 

 remaining species on the other hand (genus Megathymus). In Aegiale 

 (PI. IV. Fig. 9) the 2nd joint is long and rather evenly narrow, the 

 3rd joint very short and conical, somewhat pointed apically ; in Mega- 

 thymus (PI. IV, Fig. 10) the 2nd joint is shorter and considerably 

 stouter and the 3rd joint, while short, is not conical, but very bluntly 

 rounded. The clothing at the base of the palpi in Aegiale is largely 

 composed of triangular scales, but towards the apex the scaling is 

 almost entirely concealed by numerous long hairs which project well 

 beyond the underlying scales and lend a general rough appearance to 

 this organ ; in Megathymus the scaling is prominent from base to apex, 

 intermingled with a few scattered hairs which, however, scarcely pro- 

 ject beyond the general surface, the effect produced being much 

 smoother than in the other genus. 



In one other structural point we have noticed a marked difference 

 between hesperiaris and the remaining species ; we refer to the pulvil- 

 lus or pad on the ventral surface of the claw segment of the legs ; in 

 hesperiaris this is strongly developed, forming a large circular pad pro- 

 jecting well outward between the claws; in the other species it is 

 greatly reduced, appearing merely as a short conical projection of vary- 

 ing length and stoutness. 



In the three above mentioned morphological features, viz. the eb- 

 sence or presence of a well developed pulvillus, the shape and squam- 

 mation of the palpi, and the specialization or nonspecialization of the 

 wing venation in the male sex, we consider we have sufficient warrant 

 for holding the two genera Acgiale and Megathymus separate. 



