444 PERCY SLADEN TRUST EXPEDITION 



all of them belong undoubtedly to A. pygmcea, as defined in the Selys-Synopsis. In that 

 species the male is characterised especially by the very peculiar shape of the inferior anal 

 appendages, and in that respect our specimens agree perfectly with a series fi'om Colombo, 

 Ceylon, which Dr Ris has examined, and also with odd specimens from Australia. The 

 prothoracic lobe is very much the same in all the males which he has studied. 



The distinguishing feature of the typical pygmcea female is the form of the hind 

 margin of the prothorax. This form is unique in the genus, the margin being without a 

 backward prolongation or lobe, almost straight, and with two very minute and very 

 laterally-placed tubercles, a condition entirely different from that found in the corre- 

 sponding male. This form of the female Dr Ris has seen from Ceylon, Java, Queensland, 

 and Sydney. 



In addition to the regular males and females just considered, the Percy Sladen Trust 

 Collections contain a certain number of females which belong to an unknown form. These 

 females are characterised by the pronotum having a thin, elevated, quadrangular, and very 

 slightly emarginated median lobe, whereas the normal females are devoid of any lobe 

 whatever. At first sight, it seemed as if we were dealing here with a distinct species, 

 but, owing chiefly to the absence of any males which could be referred to a second 

 species, Dr Ris is now practically certain that these females represent a very curious 

 and interesting case of structural dimorphism. Structural dimorphism in the same sex, 

 as distinguished from colour dimorphism, is of rare occurrence in Dragonflies, but Dr Ris 

 has drawn my attention to another instance afforded by the Mediterranean Aeschnine 

 Boyeria irene Fonsc, in the female of which the terminal appendages may be either 

 long or short. Furthermore, in his newly-published monograph of " The North American 

 Dragonflies of the Genus Aeshna," Dr E. M. Walker figures variations in the length 

 and depth of abdominal segments 1- — 4, as well as variations in the length of the anal 

 appendages, in the females of certain North American species of that genus. 



In Agriocnemis, as in the closely-allied genus Ischnura, the females are subject to 

 rufous dimorphism, and the present species affords no exception to the rule. In the 

 Seychellean females, therefore, we get two distinct morphological forms, and two colour 

 phases of each form. The matter may be tabulated thus : — 



Hind-margin of prothorax not [Ground-colour of body green, ?a 

 lobed {forma typica) [Ground-colour of body orange, $6 



Hind-margin of prothorax dis- fGround-colour of body green, $c 

 tinctly lobed {forma nova) \Ground-colour of body orange, ^d 



The four females from Coetivy (1905) are all of the orange, lobed form (?c?). The 

 16 females from Mahe and Silhouette (1908 — 9) can be grouped in this way: — 



2 specimens ? a] 



2 „ ?6. 



3 „ ?c 



8 „ %d 



1 specimen of uncertain coloration 



Non-lobed 



Lobed 



