LiLLiE. — Oil New Zealand Ephemericlae. 165 



of the nervures it is likely to be occasioned by the suppression 

 of some of them. Unstable in minutiae, so closely is the 

 essential plan of neurcxtion adhered to by nearly related may- 

 flies that the general facies of the wing is an important aid 

 to classification. The nervures are numbered in the diagrams 

 as follows : 1, the costa, coincident with the anterior margin 

 of the wing; 2, the subcosta; 3, the radius; 4, the sector ; 

 5, the cubitus; 6, the praebrachial ; 7, the pobrachial ; 8, the 

 anal; 9^, 9^, &c., axillary nervures; 10, the sutural, coin- 

 cident with the inner margin. 



The nervures of the fore wing arrange themselves in three 

 groups. The first— consisting of the costa (1), the subcosta (2), 

 and the radius (3) — communicates directly with the thorax ; 

 the second— containing the sector (4), the cubitus (5), the 

 praebrachial (6), and the pobrachial (7) — is either annexed to 

 the first group, or terminates in the wmg-membrane adjacent 

 to it, close to the base of the wing; the third group — con- 

 sisting of the anal (8) and the axillary nervures (9\ 9^ &c.) 

 — is associated with the prominent curved or angulated crease 

 in the membrane which forms the boundary of a depression 

 posterior to the great cross-vein and close to the wing-roots. 

 By careful inspection of the third group of nervures, observing 

 especially the disposition of the proximal extremities of the 

 main nervures along the prominent curved fold of the mem- 

 brane, the form of the area contained by the first axillary 

 nervure and the inner margin of the wing, or of the area en- 

 closed by the first and second axillary nervures, and lastly by 

 the general aspect of the adventitious and other nervures, the 

 approximate affinities of Ephemericla to one another can be 

 ascertained very easily. Cross-veinlets are generally of small 

 account in classification. 



In the nervures of the hind wing the cubitus (6) is trans- 

 ferred from the second group, and is annexed to the radius (3), 

 the sector and other adventitious nervures either remaining 

 apart from both or forming a union with either of them. The 

 anal nervure (8) is transferred to the second group. The 

 axillary nervures forming the third group generally occupy a 

 very limited space. 



The legs present great differences, some sexual, some 

 generic. The fore legs are always longer in the male than 

 in the female, and are usually longer than either of the 

 hinder pairs. The fore tarsus is often as long as the tibia ; 

 in the male frequently much longer. The number of tarsal 

 joints is 5, or 4. The ungues of the fore tarsus are sometimes 

 alike in size and form ; often unlike. 



The forceps of the male are 2-, 3-, or 4-jointed, with the 

 basal joint, or the next, longest. In some genera they afford 

 good distinctive characters of species. 



