ONISCIGASTEE WAKEFIELDI. 141 



slender and white, excepting the more robust basal joint, which is 

 brownish. 



The female subimago differs in the body being greyish rather 

 than a decided brown ; and the winga are uniformly smoky-grey 

 (the anterior pair paler at the base), which coloration is caused 

 by the subimaginal pelJicle. I give here an extended specific 

 diagnosis. 



Oniscigastkr Wakefieldi. 



( 5 Imago.) O supra nigro-fusca ; thorace nitido ; abdomine indistincte 

 pnllido-vario, infra flavido, nigro-punctato, segmentis singulatim 

 macula magna nigra utrinque signatis : caudjE flavo-albidse. Pedes 

 flavi, late nigro-annulati. Alae vitrese, anticarum dimidio basali et 

 posticis omnino laete fuliginosis : venae veuulseque nigrae ; his ad 

 anticarum marginem costalem valde incrassatis, nigro-marginatis et 

 suffusis : humeris nigris vel nigro-fuscis. 



Long. Corp. (sine caudis) 10'" (=21 mill.); exp. alar. 19'" (=40 

 mill.). 



( § Subimago.) Corpus griseum vel fusco-griseum. Alee subopacse, 

 griseo-infumatae (anticae ad basin pallidiores) ; venis ut in $ colo- 

 ratis. 



( (S Imago.) Corpus pauUo minus robustum ; appendicibus albis, articulo 

 prime robusto, paullo fusco-tincto, 2° parvo, 3° valde elongate, gracili, 

 curvato, 4° et 5° brevissimis, aequalibus ; peni elongate triangulari, 

 fusco, ad apicem exciso. Long. cerp. (sine caudis) 9^'" (=19 mill.) ; 

 long. caud. extern, circa S"' (=1/ mill.); medianae 2^'" (= 5 mill.) ; 

 exp. alar. 16^'" (=35 mill.). 



The value of Mr. "Wakefield's last consignment was greatly 

 increased, inasmuch as accompanying it were two individuals of 

 the aquatic conditions of the insects in spirits. These are so 

 interesting that a somewhat detailed description is necessary. 

 They are of difierent ages, and may be termed 'larva' and 

 ' nymph ' respectively, though, as is well known, these stages are 

 defined in the Ephemeridse by no abrupt line of demarcation such 

 as exists in the life -history of insects with more complete meta- 

 morphosis. I use the terms as a matter of convenience, because 

 the larger individual has strongly developed rudimentary wings, 

 and is evidently nearly mature, whereas the smaller only pos- 

 sesses the thoracic lobes which indicate the position of the 

 wings. 



I proceed to consider the larger individual, or " nymph," first. 



It is 12^'" (=26 mill.) in length including the tails, and 0'" 



