670 Dr. T. A. Chapman on an 



ab. icarinus from the North Downs taken by Mr. 

 Grosvenor that look like fhcrsitcs rather than icariis and 

 are strongly marked and coloured, and that as regards 

 the post-discal row of spots, Freyer's figures of icarus, 

 pi. 616, have this row of spots more in the disposition 

 usual in thersites than is shown in his figure of alexins, 

 pi. 676. 



The point as to which Freyer's figures are indecisive 

 has reference to the apical spots of the hindwing. This is 

 not referred to in the text, and its precise representation 

 may easily have been left to the artist. 



One important result of having obtained such an 

 accession of material as the Tutt series, is that I am 

 able to point out those differences in markings between 

 thersites and icarus (with its var. icarinus) that are fairly, 

 if not quite constant, and will perhaps enable the 

 entomologist, who likes something he can easily see, to 

 appreciate the specific distinctions of the two insects. 



One very obvious difference in the markings of icarus 

 and of thersites that is sufficiently constant to enable the 

 great majority of thersites to be distinguished from icarus, 

 apart from the basal spots, is the relation of the apical 

 orange spot of the hindwing beneath to the two first spots 

 of the post-discal row. 



In thersites, the black line bounding this spot basally, 

 is level with the second post-discal spot, and it results 

 that its distance from the first post-discal spot is about 

 equal to that between the first and second spots. It may 

 even be rather nearer the first spot than the second is. 

 It is rarely further away and never markedly so. 



In icarus, the black line of the apical orange spot is 

 further from the base than the second discal spot, and so 

 is obviously further from the first discal spot than the 

 second one is. The position of the orange spot varies 

 more in icarus than in thersites; and so specimens are not 

 rare in which it occupies much the average position that 

 it does in thersites, and may be even nearer the base. 

 Nevertheless few errors would be made in separating the 

 two species by this character without reference to the 

 basal spots of the forewing (pi. LXXXI). 



In none of our other common blues does this orange 

 spot take up the position it has in thersites. In thetis, 

 corydon, eros, hylas, eseheri, etc., it is as far or further from 

 the base than in icarus. 



