THE "LOUISA" DRAGON-FLY. 179 



black : the abdomen is black, and composed of segments 

 laterally spotted with vellow. 



The Libellula, which the illustrious Geoffrey designates 

 " Louisa," is, according to modern entomologists, neither a 

 Libellula nor a Aeshna, but an species tf Agarion, the Agarion 

 virgo (Libellula virgo, Linn.) The Agarions are distinguish- 

 able from the Libellula and the Aeshna by their remarkably 

 thin, filiform, and exceedingly elongated abdomen, and by 

 the three ocelli arranged triangle-wise on the top of the 

 head. 



The " Louisa" (Agarion virgo) is by no means uncommon 

 in England, and may be found along the upper course of the 

 Thames, the Avon, and other rivers. 

 It is easily recognised by its frail 

 slender body, shining with metallic 

 blue reflexes. There are numerous 

 varieties, distinguished by their va- 

 rieties of "light and shade." The 

 spotless green-winged species is the 

 "Ulrica" of Geoffrey. The two 



FiG. 38. Male and Female of 



sexes are not alike. In the centre \h* Agario vir&. 



of their delicately-reticulated wings the males have a large 



bluish-brown spot, which is wanting in the females. 



The genera Libellula, Aeshna, and Agarion compose the small 

 family of the Libellulites a family plainly and conspicuously 

 characterised by the size of their head, and by the two pairs 

 of diaphanous wings of almost equal dimensions (the posterior 



