1873.] ■ 109 



by foreign elements that there find conditiona more suited to them 

 than even their places o£ origin, it at least furnishes us from time to 

 time with most remarkable forms in all classes. Not one of the less 

 conspicuous of these is the extraordinary ' May-fly ' described beloWy 

 which I recently received from my friend C. M. Wakefield, Esq., of 

 Christchurch, Canterbury Settlement, N.Z.* 



ONISGIGASTEB. 



( $ Imago). Corpus elongatum, valde rohustum. Alee quaiuor ; 

 posticce sat latcs, ovales ; omnes venulis transversalibus ubique (anficcB 

 apicem versus minus dense) regiilariter reticulatcB. Pedes antici reliquis 

 vix longiores ; tarsi omnes 5-arficulafi, suh-cequalifer hiunguiculatiypos- 

 ticorum articulo 4° hrevi sed valde distincto. Abdomen valde elongaium 

 et rohustum ; segmentis 7° — 9° utrinque conspicue corneo-alatis, acute 

 producfisf ; ultimo parvo, elongato, obtuso-conicale : ovivalvula nulla : 

 caudcd tres elongatae (mutilatce, sed mediand cceteris graciliore, ef forte 

 breviore) . 



The extraordinary abdomen of this genus, if considered without 

 regard to the rest of the body, might almost pardonably be mistaken 

 for that of some Myriapod (without the legs) or Crustacean. In the 

 absence of the (J , the afiinities must remain somewhat uncertain;}; ; 

 but, on the whole, I think that Ephemera (as restricted) and Pentagenia 

 may be considered as the nearest allies, both of these differing (putting 

 the abdominal characters for the moment out of consideration) in 

 having only 4-jointed posterior tarsi. Sipliluriis agrees in possessing 

 5- jointed posterior tarsi, but differs in its rudimentary (or, it may be said, 

 absent) middle tail. Mr. Eaton has 'pointed out in his Monograph of 

 the EpliemeridcB, that a tendency to lateral production of the terminal 

 segments of the abdomen is shown in several genera, but the amount of 

 expansion hitherto known is infinitesimal as compared with that present 

 in Oniscigaster. For actual affinity in this respect we must look to the 

 aquatic stages of some forms ; and if the assertion by MM. Joly, that the 

 so-called genus of branchiopod Crustacea named Prosopistovia by 

 Latreille, is, as appears most probable, in reality only the aquatic con- 

 dition of an Ephemerid, we have in the " Binocle a queue en plumet ' 

 the nearest ally, so far as regards abdominal structure, to Oniscigaster. 



* Almost immediately before receiving the insect to the consideration of which this paper is 

 devoted, I had published in the " Annals and Magazine of Natural History " for July, 1873 (pp. 

 30—42), a list of all the then known species of Nevu-opterous Insects from New Zealand. — R. MuL. 



t In one of the examples mentioned at p. 110, there is also an irregfular and very acute projec- 

 tion on the right-hand side of the 6th segment. — R. McL. 



% From analogy, it may be considered almost certain that the i will prove to have long an- 

 terior legs, a still shorter middle tail, a less robust abdomen, with probably still greater develop- 

 ment of the lateral processes, and the usual anal forceps. The eyes are probably simple, as iii< 

 Ephemera, &c.— R. McL. 



