POLYOMMATUS. Ill 



4. The sedoeagus is almost the same in the two species of Agriades (thetis and 

 coridon), in which it is slightly bulbous, and its membranous attachment to the 

 other appendages is similar, and it has only a very short portion beyond. In 

 Polyommatus (icarus) it is more slender, rather angular at its point of attachment, 

 and has a portion of considerable length beyond. This is perhaps the most 

 striking difference that can be detected between Polyommatus (icarus) and the two 

 species of Agriades (thetis and coridon). 



Whilst the genitalic differences between Polyommatus and Agriades 

 must be considered as exceedingly close, those of Aricia and Polyom- 

 matus, the species of which are usually thrown together, are remark- 

 ably distinct, in fact, as already pointed out in the preceding volume 

 (p. 156), Aricia is, after Plebeius, the most separable and distinct 

 section with British representatives of the tribe Plebeiidi. There is 

 no need to repeat here the differential characters of Aricia as there 

 noted, and it will be readily granted that these differences clearly 

 support the generic separation of the latter genus from Polyommatus. 

 As comparative differential characters, Chapman notes (in litt.) the 

 following details : — 



1. The dorsal portion is, in Aricia (astrarche), narrower, or at least so 

 oriented as not to be easily spread out as that of Polyommatus (icarus) can. The 

 ridge noted in Polyommatus (icarus) as somewhat transverse, and more longi- 

 tudinal in Agriades (coridon), is, in Aricia, if it be the same ridge, longitudinal, 

 but proceeds from the tip of the process, and has a remarkable bend in its middle. 

 The hooks are smaller in Aricia (astrarche) , with a broad basal portion, and with 

 the distal portion narrow, yet not tapering, but, indeed, with a rather broader 

 wider point. 



2. In Aricia (astrarche) the serrated end of the clasp has not the scimitar 

 outline of Agriades (coridon, thetis) or Polyommatus (icarus), but is simply tapered 

 with a rounded end, and seems much less a separate portion of the clasp than in 

 these species. The clasp of Aricia (astrarche) is specially remarkable amongst 

 Plebeiid genera, in having along one surface down the middle of more than its 

 distal half, rows of points or serrations, or raised spines, whose actual site would 

 seem to be the opposite margins of the soft and spinous portions of the clasp, albeit 

 these two portions are here very closely amalgamated, and not clearly dis- 

 tinguishable. 



3. Another very distinctive structure is the aedoeagus, which, instead of the 

 short square (roughly speaking) outline seen in those of Agriades (coridon) and 

 Polyommatus (icarus), tapers in Aricia (astrarche) from its base, to a very sharp 

 point, and of this length more than half is beyond the membranous attachment 

 which is marked by chitinous projections. 



We have already noted (supra) Chapman's remark on the difference in 

 the sedceagus of Polyommatus (icarus) and that of Agriades (coridon and 

 thetis). He deals (Ent, Hec, xxii., pp. 101 et seq.) with the matter at 

 length, noting among other interesting details that " the aedoeagus 

 affords very distinct forms in Agriades {coridon, etc.) and Polyommatus 

 (icarus, etc.), and separates these two genera, for which, at present, 

 no differentiating characters have been proposed." He then states 

 that, of the Plebeiid genera, Agriades has, perhaps, the most easily 

 recognised form of asdceagus, well seen (antea, vol. x., pi. xxi., fig. 4), 

 as a straight shaft, with a contracted neck at the base, but, most 

 characteristically, a bulbous swelling at the top. Further, in Agriades, 

 the aedoeagus is attached to the floor of the genital cavity, through 

 which it passes, in a zone that is on the bulbous swelling near its lower 

 margin, so that the portion of the organ above the membrane is 

 merely the upper part of the bulb and a small projection beyond the 

 zone of attachment. Polyommatus agrees with Agriadesin having a com- 

 paratively small portion beyond, but this portion is a shade longer, and 

 differs entirely in that it tapers from the zone onwards, and has no trace 



