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one feeds upon a plant so different from the food upon which the 

 other is found, that probably the food of the one would poison the 

 other, it appears to me that the specific distinctions between the two 

 insects may be regarded as established. 



We have, however, P. Sahnacis still remaining undetermined, its 

 caterpillar and chrysalis not having as yet been found. The chief 

 distinction to be remarked in its external character is the slight but 

 peculiar areola of white scales which surround the black spot occu- 

 pying an exactly similar position in the upper wing as in Agestis. 

 Although Mr Doubleday regards this insect as a variety of P. Ar- 

 taxerxes, I have always felt and still believe it to be much more 

 closely allied to P. Agestis. During last year (1855) I visited Castle- 

 Eden-Dene, the habitat of P. Salmads, Sind bearing in mind my obser- 

 vations on Arthur's Seat, felt sure I should by digging in similar 

 places under the tufts of Helianthemum find the chrysalids. In 

 this I was unsuccessful, although the Helianthemum was most abun- 

 dant. The spot on which P. Salmacis is found faces the sea (the Ger- 

 man Ocean), and the ground is a stiff wet clay, with dense, coarse 

 herbage, both ill suited for burying its chrysalid, if that be its habit ; 

 nor is the Helianthemum the prevailing plant there. Mr Wailes ob- 

 serves, that he has never found it more inland than a quarter of a 

 mile from the sea ; and although the Helianthemum is most abundant 

 in the upper part of the Dene, Mr Tristram, the clergyman of the 

 district, and other residents, assured me it was never seen except on 

 the spot I have named, by a high cliff of clay overhanging the sea. 

 This certainly suggests the idea of its being dependent on some lit- 

 toral plant growing only within a certain range of the salt water. 

 I observed the Anthrocara Jilipendula and Procris statices flying 

 in great numbers together with P. Salmacis, and their chrysalids at- 

 tached to the stems of plants were abundant. I did not at the time 

 know of Mr Harding's observations, and that P. Agestis fed upon 

 Erodium cicutarium, and, consequently, did not particularly note 

 whether that plant grew there ; but having been accustomed to bota- 

 nical observations all my life, I think 1 should certainly have noticed 

 it if it had been the prevailing plant, — a thing, moreover, which the 

 stiff clay soil renders improbable. What I did notice was the Gera- 

 nium sanguineum in great quantity (the flowers filled with Ceutorhyn- 

 chus geranii), a plant not far removed in natural affinity from the one 

 I have just named. Altogether, I feel inclined to predict that P. 



