664 Dr. T. A. Chapman on an 



are, however, other localities in which the two species 

 seem to be quite independent. 



The definite distinction between thersites and icarus, 

 which first attracted my attention, was in the male 

 appendages. No doubt the chief reason that the species 

 has for so long been refused recognition is that apart 

 from the genitalia (both sexes) and the androconia, no 

 character can be stated that absolutely and certainly 

 distinguishes thersites from icarus, though there are some 

 points that are very useful for that purpose. 



It would appear that no one has chosen hitherto to 

 examine either the genitalia or the androconia of the 

 species, certainly not comparatively with those of icarus. 



The whole of the Plebeiid blues have a very similar 

 form of appendages in the male, and in some species 

 there is a considerable range of variation in some par- 

 ticulars, so that there is, in such cases, a difficulty in 

 seizing constant points by which to separate allied species. 

 In the present case, however, no such difficulty arises, as 

 the differences between the two species are such as are 

 not only of decided specific value, but actually of generic, 

 or at any rate of subgeneric importance, placing icarus in 

 the genus Folyommatus, Latr., and thersites in Agriacles, 

 Hb., accepting these genera as adopted by Tutt, who 

 distinguished between them before the differences in the 

 genitalia were noted. 



I have made camera sketches of the most important 

 (for differential purposes) structures in icarus, thersites 

 and in escheri. 



The form of the Aedeagus is very different in icarus 

 (Polyommatus) from that in thersites and escheri {Agriades). 

 It will be noted that thersites and escheri are almost 

 identical except in size, escheri being decidedly larger as 

 6 to 5. The dorsal hooks also differ notably, the portion 

 that is upright in the sketches is broader basally and 

 tapers more regularly in icarus and is fairly straight 

 terminally. In thersites and escheri it is comparatively 

 narrow basally, tapers more slowly, and has a hooked 

 curve at the end, it is and looks longer and more slender 

 than in icarus. As in the aedeagus, thersites is here dis- 

 tinctly smaller than escheri, as it is in the other portions 

 of the appendages. 



What is the relation of thersites to escheri ? The genitalia 

 appear to be the same except in a constant difference in 



