AGRIADES THETIS. 331 



faint traces of chequers. Underside very like some examples of Polyommatus 

 icarus with clear white discoidal spot on hindwings. Kent, June, 1886 (South, 

 Ent., xx., p. 80). 



o. — ? . Ground colour of a pale uniform washed-out khaki-yellow on both 

 sides, with faint marginal lunules round all the wings. Yienne = cdbinismo- 

 rufescens, Obth., Lep. Comp., fasc. 3, p. 407, pi. xix., fig. 63 (1909). 



Webb notes Ent., xxi., p. 134) that an occasional form of aberration 

 of almost annual occurrence, appears to be a defect in the mature 

 scaling of the wings, which causes the insects affected to look shining, 

 almost as though they had been dipped in oil. 



Variation. — The variation of this species is considerable, although 

 purely racial forms are much less frequent than in the allied Agriades 

 eoridon. The different shades of the ground colour of the $ s, usually 

 of the most brilliant hue, are most difficult to differentiate in words. 

 One distinguishes in any ordinarily long series captured in Britain, at 

 least four distinct shades : — 



1. Brilliant shiny, silky, or pearly-blue = excelsia, n. ab. 



2. Brilliant shining sky-blue = adonis, Schiff. 



3. Brilliant shiny blue, with a slight tinge of purple (or violet) = bellargus, 

 v. Kott. 



4. Brilliant shiny blue, strongly tinged with purple (or violet) —purpurascens, 

 n. ab. 



Besides these, there are several other described forms, e.g., (1) 

 silvery-grey = ab. argentea, Obth.; (2) pale lavender or pale lilac = ab. 

 pallida, Aust.; (3) bluish-grey = ab. czekelii, Aign.-Abali; (4) leaden-blue 

 = ab. nigra, Ckll. There is some ground for believing that the two 

 last-named may also be produced artificially. Pickett (Proc. South 

 Lond. Ent. Soc, 1906, p. 47), Hodgson (op. cit., 1908, p. 46), and 

 others, speak of a greenish-blue form ( = ab. viridescens, n. ab.), and 

 Prideaux observes (in litt.) that specimens taken at Seaton, September 

 1891, showed, on the average, a decidedly greener shade of blue than 

 specimens from Surrey or the Isle of Wight. There is occasionally 

 some suggestion of racial tendency in developing a particular form of 

 ground colour locally, e.g., the Mauretanian examples are distinctly 

 purple- blue; the Canales examples, violet-blue (Chapman); the $ s 

 from Charente-Inferieure, bright sky-blue, like that of Polyommatus 

 hylas (Blachier), and so on. There are some very purple-blue 

 specimens in the British Museum coll., from Bergiin, Zurich, etc. 

 The nervures in the $ s are usually pearly-white towards the base, 

 frequently becoming black towards the outer margin, so that the dark 

 dashes in the fringes appear to be continuations of the nervures ; the 

 dark dashes, however, are sometimes much less strongly developed on 

 the hindwings than on the forewings, and are reported as occasionally 

 absent altogether, but, judging from the great number of specimens 

 examined without finding a single example, this extreme form (ab. 

 liyacinthus, Lewin) must be rare; Blachier notes (in litt.) that S s in 

 his collection from Charente-Inferieure and Veyrier (near Geneva), 

 have the fringes almost pure white, scarcely chequered with black, only 

 an extremely fine line passes through the fringes as a prolongation of 

 each nervure. In some examples, a trace of a series of interneural 

 marginal spots is found on the hindwings of the S s, sometimes 

 developed into a well-defined row of small, roundish, black dots ( = ab. 

 puncta, Tutt). This character is often strikingly developed in the large 

 Mauretanian race, pnnctifera, Obth., although the latter is not merely 



