164 Transactions. — Zoology. 



Aet. XX. — On Neio Zealand Ephemeridae : Two Species. 



By C. 0. LiLLiE, M.A., B.Sc. 



[Bead before the Otago Institute, 15th November, 1898.'] 



Plates XIV.-XIX. 



The EphemeridcB are insects with a long, soft, 10-jointed 

 abdomen, furnished at its hinder end with either two or three 

 many-jointed setaceous or fiHform tails (caudal setae). The 

 body is smooth and glabrous. The head is free, with 

 atrophied mouth - organs and carinated epistoma ; short 

 subulate antennae, composed of 2 or 3 short stout joints, 

 succeeded by a many-jointed setaceous awn, three ocelli, and 

 large oculi (compound eyes). Thorax robust, mesothorax 

 predominant, sternum well developed ; fore wings ample, 

 erect or spreading in repose, slightly plaited lengthwise ; 

 legs slender, femora strong, the fore coxae somewhat distant 

 from the others. The abdomen in the male armed with a 

 pair of claspers (forceps) placed ventrally at the extremity of 

 the penultimate segment ; the vasa deferentia have each a 

 separate intromittent organ, situated at the ventral joining of 

 the ninth and tenth segments. 



Peculiarities in structural detail are often noticeable in 

 both or one of the sexes, and are chiefly presented by the 

 ocelli, wings, legs, and caudal setae ; and in the male by the 

 ocelli and forceps. The ocelli are always much larger in the 

 male than in the female, and are divided into two parts trans- 

 versely ; the upper portion has larger facets than the lower, 

 and is sometmies coloured differently. 



The fore wings are usually trilateral, ample and rounded 

 off at the extremities ; they are relatively longer in the 

 female. The hind wings in some of the genera are not 

 developed ; in others they are very minute ; and generally 

 they are not very large. Their usual form is triangular-ovate, 

 or oblong-ovate, with a salient prominence in front, either 

 close to the wing-roots or midway towards the apex, in which 

 case the prominence is sometimes followed by a deep de- 

 pression. Their neuration is fairly plentiful. The inner 

 margin of the fore wing and the anterior margin of the hind 

 wing hitch together automatically to a larger or smaller extent 

 when the wings are spread open. The wing-membrane is 

 usually glassy or iridescent in the adult. Wing-neuration in 

 the EphemeridcB is less complicated than it appears to be, and 

 when difficulty is experienced in ascertaining the homologies 



