THE ENTOMOLOGIST. 27 



exhibiting specimens of Papilionidae to illustrate his views: 

 on this occasion he relied chiefly on altered form, as, on the 

 former occasion, on altered colour : great discrepancy was 

 observable in the outline of the costa, the normal form being 

 a gradual curve from the base to the distal extremity, and 

 the aberrant form exhibiting a much more arcuate outline, 

 and in some instances a very decided bend at about a third 

 of the length from the base. Mr. Wallace, in a speech 

 fraught with the most interesting observations, proposed to 

 account for the prevalence of this highly arcuate and bent 

 outline, on the Darwinian hypothesis that, in the insular 

 localities vsdiere such forms occurred, the individuals possess- 

 ing the normal form had been destroyed by their natural 

 enemies, leaving only those which possessed some pecu- 

 liarity, as rapidity of flight, obscurity of colour, pungency of 

 scent, &c., to protect them : in the instance of the butterflies 

 he exhibited he thought that the abnormal outline of the 

 costa might give them greater power and rapidity of flight. 

 The President asked whether Mr. Wallace had ever seen 

 these butterflies pursued when on the wing, and was answered 

 in the negative. Captain Cox and Mr. Newman contended 

 that the contour of the wing, as pointed out by Mr. Wallace, 

 was -not by any means accompanied by rapidity of flight ; but 

 that the most rapidly flying insects usually possessed a 

 straight costa; thus the Diptera were the most rapid of 

 flyers, and among the Lepidoptera the Sphingidae deserved the 

 palm in this respect ; and among the Sphingidae the straight- 

 winged genera, as Macroglossa, were much more rapid than 

 such species as Smerinthus Populi, which was the slowest 

 among Sphingidae, although it possessed the most decidedly 

 arched costa. Mr. Smith took the same view, and instanced 

 the Hymenopteron, Astata boops, as a most rapid flyer with 

 straight costa. 



Hydrilla palustris. — At the May Meeting of the Entomo- 

 logical Society, Mr. Dunning (on behalf of Mr. R. S. Schol- 

 field, who was present as a visitor) exhibited a specimen «f 

 Hydrilla palustris, captured by Mr. Scholfield in Quy Fen, 

 Cambridgeshire ; the specimen was a male, and was dis- 

 turbed from grass on the afternoon of the 29th of May, 1862. 

 This Noctua was introduced into the British list on the 



