414 On the genus cordulephyA, 



mountains, and one on the coast also, but the mountain-form 

 {M. i/i/ffafa) is smaller than the corresponding coastal form 

 (ill . guttata, var. 2^«//if/a) ; and finally two species of Ghoris- 

 thertiis, both coastal forms only, and both distinctly more 

 specialised than the other species. For the other example, 1 

 take Synlestes wcyersi, a species that shews a remarkable 

 gradation of venational forms. Specimens from the Blue 

 Mountains are much larger and more densely reticulated than 

 the coastal forms, and a series from different localities can be 

 arranged to shew jfof/ressive sjjecialisation by reduction, in a 

 most perfect manner. 



Comparing now the venation of Cordulephya montana and 

 C. pygmca, wc see, at once, that the mountain-form (C 

 /t/oiifana) is the less reduced. The point specially to be 

 noticed here is, that all this evidence is in favour of the 

 "quadrilateral" triangle of Cordulephya being "not primi- 

 tive, but secondarily derived from a three-sided one, and an 

 extreme case of specialisation."* (I quote the very words 

 used by Needham on the four-sided triangle of PentathemAs). 

 We may svippose that the two closely allied species now 

 existing were, in the near past, one single species, with a 

 range probably including that of the two, or of even greater 

 extent. It is, moreover, extremely probable that this species 

 had a completely or almost comjjletely recessed hindwing- 

 triangle. One portion of this species, located in the movxn- 

 tains, was not faced with such a strenuovis task as the other 

 portion, that along the coast. The latter, left to fight the 

 invaders on its own ground, and, as it were, being placed in 

 the forefront of the conflict, had either to be exterminated, 

 or to conserve its resources so as to make a successful fight. 

 The line of defence adopted is a well-known one, and had 

 already been carried out more completely amongst the 

 Odonata, by practically the whole of the Gcenagrionince; viz., 

 defence by reduction, conservation of force and material, and 



* Loc. cit., p. 276. 



