14 HEV. A. E. EATON ON liECENT EPIIEMERID.E OE MAYPLIES. 



Second raaxillsc, when present (in OUgoneuria they are either suppressed, or else are 

 reduced to the condition of raised folds traversing- the upper surface of the lahium, 

 PL XXVI.), simple and usually flattened ; palpus 2-jointed in allies of Palingenia and 

 Ecdyurus (though in this latter group of genera the last joint may essentially be 

 compounded of two), 3-jointed in most other instances, but in one remarkable case 

 (PI. LIV.) multiarticulate ; it usually tapers towards its extremity, but is sometimes 

 enlarged or expanded, whilst in BcBtisca (PL LII.) it is actually forcipate. Labium 

 in the large majority of genera plane and bipartite, with lobes as large as, or smaller 

 than, the lacinise of the second maxillae. In a few cases it is undivided, and is then 

 either plane and creased lengthwise through the raxMlQ {Oligonenr'm, PL XXVI. ), or 

 else is conduplicate {FaUngenia, PL XXV. ; ToJumltareys, PL XXVIIL). Tongue 

 (glossa) and paraglossa? membranous or pergamentose, the former usually inflated and 

 often concave in the middle, generally broad, and citlicr as long as or shorter than the 

 paraglossse. The following are their leading modifications : — paraglossse broad ; tongue 

 ovate (Pis. XXV. & XXVI. , Pctllngenia ani OUgoneuria), subrotund (PL XXVII. JoUa), 

 oblong and entire (PL XXXIII. Bla'sturus), emarginate (Pis. XXIX. & XXX., Eiifhy- 

 plocia and Ephemera), obcordate (PL XXXI. Poiamanthns), retuse, with claw-like lateral 

 projections (Pis. XXXIV. & XXXV., Ghorotcrpes and Thraiilus), raucrouate, and in 

 combination with the paraglosste rather like a mitre or a birctta seen broad-wise 

 (Pis. XLV.-XLVII., Bai'tis and allies) : — paraglossaj narrow and recurved, tongue 

 broad and bifid (PL XXXVI. , Habropldebia). In some genera both glossa and para- 

 glossa) appear to be absent ; Prosopistoma seems to have none. 



Thorax compact or subcompact, rigid ; pectus rather broad ; prothorax usually well 

 developed and more distinct than the metathorax from the mesothorax ; but in Baitisca 

 and some few other genera (Pis. XLIIL, LII.) the pronotum is intimately blended with 

 the mesonotum. Ecdyurus and many of its kindred have the head and pronotum bordered 

 at the sides with a membranous expansion seemingly subservient to the oxygenation of 

 intratracheal air. The winglets of advanced nymphs are united by their inner margins 

 to the apical borders of their proper segments, and overlie the base of the abdomen. In 

 nearly mature nymphs of OUgoneuria (PL XXVI.), and in even less aged specimens 

 of genera related to EphemereUa (Pis. XXXVII.-XL.), the space included between 

 the terminal margins of the fore wings and the peak of the mesonotum becomes closed 

 over by a membrane in continuity with the same, extending almost up to the extre- 

 mities of the wings. This membrane is produced backwards still farther in Prosopistoma 

 and Bcetisca (Pis. XLIII. & LII.), so as to form in combination with the wings a 

 hood which completely roofs over the tracheal branchiaj and the segments that bear 

 them. Pormerly the construction of this shield was not quite understood, the whole of 

 it being attributed to hypertrophy of the mesonotum ; but one of Dr. Hagen's gifts of 

 specimens furnished the means of explaining its composition rightly. Coxa) usually 

 prominent, but not so in Prosojnstoma (I. <?.). Trochanter short and strong. Femora 

 moderately or very stout, sometimes much compressed. Tibia) spurless, though in a few 

 instances terminating in a point or spine ; often apparently compound owing to the 

 distinctness of an oblique line of muscular insertion perceptible below the knee. Tarsi 



