EEV. A. E. EATON ON EECENT EPHEMEEID.E OR MAYFLIES. 319 



'Hw.' Tracheal brancliire bifid, with filifornily dissected divisions . . Hahrophlebia, j). 115, PI. XXXVI. 



13. Foremost tracheal brancliise bifid, with linear-lanceolate divisions : the others consist of 

 jugate, obliquely subovate, tail-pointed, fringeless, foliaceous lamiute. Blasturus, p. 100, PI. XXXIII. 



., Foremost tracheal branchiae single, linear-lanceolate ; the others composed each of two jugate, 

 unequal, cuspidate, foliaceous lamiuic, oblique at the base, of which laminffi the smaller is 

 obliquely ovate, and the larger obliquely subcordatc-ovate, with unequal auricles : the cusps are 

 discontinuous with the blades of the laminte Choroterpes, p. 105, PI. XXXIV. 



.. Foremost tracheal branchiae bipartite, with filiform divisions : the others composed each of 

 two jugate, oblong-ovate, fimbriate, foliaceous lamina; Thrauhis, p. 107, PI. XXXV. 



14. Four or five pairs of abdominal tracheal branchiai. Palpus of maxilla i shorter than the lacinia 15 

 .. Six pairs of abdominal tracheal branchiae. Palpus of maxilla i longer than the lacinia . . 16 

 .. Seven pairs of abdominal tracheal branchia;. Palpus of maxilla i equal in length to, or 



longer than, the lacinia 18 



15. Pronotum well developed. Palpi of maxillae ii simply pointed. Hinder tracheal branchiae 

 each composed of a lamina, concave on the underside, sheltering a partly adherent forked 

 appendage beset with membranous lamellae. At maturity triangular membranes extend from 

 the terminal margins of the fore wings to the peak of the mesouotum. Type of Ephemerella. 



See Tabulation, p. 123, Pis. XXXVII.-XL. & LXIV. (part). 

 .. Pronotum reduced to a minimum. Palpi of maxilhc ii forcipate. Tracheal branchiae at 

 maturity concealed by a large mesonotal shield, in which the fore wings are immersed. 



Bcetisca, p. 226, PI. LII. 



16. Foremost tracheal branchiae rudimentary, subulate ; the second pair elytroidal, sheltering the 

 hinder pairs, the laminae of which are fimbriate 17 



.. Abdominal tracheal laminaj imbricate, all lamellar and pergamentosc : the foremost is 

 triangular-obovate in form ; each of the other laminae is somewhat oval, with a large rounded 

 foliated, eroded and laciniate lobe produced from its interior margin. Abdominal pleura 

 oniscoidally dilated Onisciff aster, p. 224, PI. LI. 



17. Laminae of the hinder pairs of tracheal branchiaj each furnished on the underside with a 



, „ filamentosely dissected appendage Trlconjthus (?), p. 138, PI. XLI. 



I „ Hinder tracheal brauchife unprovided with any appendage Canis, p. 141, PI. XLII. 



18. Lobes of the labium broad and obtuse. Pleura of the intermediate abdominal segments 



I more or less narrowly dilated oniscoidally 19 



I .. Lobes of the labium narrow and acute or falcate. Pleura of the intermediate abdominal 



segments hardly at all produced. — Type of Baetis . . See Tabulation, p. 155, Pis. XLV.-XLVIII. 



19. Abdominal tracheal branchiae all single and obovate. Palpus of maxilla i subequal in length 

 to the subquadrate lacinia, the crown of which is singularly beset with suberect pectinate spinules. 



Chirotonetes (?), p. 204, PI. XLIX. 

 .. Abdominal tracheal branchite of the first two pairs, each formed of two foliaceous laminae 

 connate at the base : the laminae of the other pairs are single. Palpus of maxilla i longer 

 than the lacinia, which is longer than broad Siphlurus, p. 215, PI. L. 



SECOND SERIES. — ZOOLOGY, VOL. III. 43 



