EEV. A. E. EATON OX EECENT EPHEMEEID.E OR MATELIES. 199 



blotch that encloses a clear space ; another irregular band extends some distance in 

 proximity to the terminal margin and subparallel therewith. At the terminal margin, 

 the interneural veinlets are single. Hind wings perfectly clear. 



$ . The markings of the wings correspond somew hat with those of the other sex ; but 

 the bauds are more perfectly defined, though faiuter in colour, and both they and the 

 blotches are broader ; hence the clear spaces are much smaller. Posteriorly the whole 

 of the wing-membrane has a smoky tint. Eyes pearl-grey, each traversed horizontally 

 by a black line; the remainder of the head and thorax yellow-grey, with the 'appendi- 

 cular organs ' almost colourless. Length of body 8-10 ; expanse of wings 16 ; length 

 of setfe, d im. 15, $ im. 12 mm. 



Hab. Cordova, Argentine Republic ; commonly, but not exclusively, in the autumn. 

 [After Weyenbergh, abstract translation, and partly based upon his figures.] 



Group III. of tue Genera of the Ephemerid^. 



Adult. — At the fore-wing roots the anal (8) communicates with the pobruchial (7) 

 nervure by a well-defined channel of circulation in the membrane ; and the first axillar 

 (9^) nervure, detached from its own group of nervaires, either meets or is very closely 

 approximated to the anal nervure at the l)ase of the wing. [In Bcetisca it is subparallel 

 with the anal, but nearer to it than to the second axillar nervure.] Legs all functional ; 

 hinder tarsi distinctly 5-jointed [the fifth joint in Colohnras is less distinct than is 

 usualj ; ungues rather small. Contour of 6 oculi either evenly rounded or obsoletely 

 ascalaphoid. Ni/i/ijjh. — the structure of the palpi varies with the Series. 



Firsi Series of Groiq) HI. 

 Adult. — Anal-axillar interspace [\>. 81, 1. G from bo(tom~\ of the fore wing curvilinear- 

 trilateral, subtended by the outer half of the inner margin and the anal angle [in BcBtlsca 

 closed by the terminal margin, and narrowly su1)linear in form] ; the intercalary 

 nervures of this interspace, varying in number with the individual, constitute simple or 

 divided branchlets of the anal [in Bcetisca tlie second axillar (9-)] nervure, and as a rule 

 are entirely free from cross veinlets distinctly recognizable as such. The structure of 

 the thoracic spiracles of many of the genera (owing to their valves being closed in the 

 dried examples exclusively obtainable for examination) has not been ascertained in a 

 manner sufficiently satisfactory for descriptive purposes, and is therefore taken only 

 tacitly into account here. Pronotum of $ , when Avell developed, transverse, longitu- 

 iinally carinate, appressed closely to the mesonotum, and more or less broadly retiexed 

 it the sides to a maximum not exceeding double its minimum extent. Eorceps-basis of 

 S , and the homologous ventral lobe of ? , usually well developed ; but the latter is small 

 n Siphlurus and absent in Oniscigaster. Oculi of S either evenly contoured or 

 )bsoletely ascalaphoid ; anterior ocellus rather smaller than the others. Subimago 

 [uiescent many hours ; its posture has been observed in only a few of the genera. 

 \"ymp]i. — Palpi of both pairs of the maxilla triarticulate. Abdominal tracheal branchiae, 

 t^hen exposed, foliaceous, friugeless, and without fasciculated fibrils at the base; those 



