on the Hphemeride. 135 
Isonychia ignota. 
(Genitalia maris, Pl. VI. fig. 29.) 
Baetis ignota, Walk. 1853. 
Imago, v.s.s.  ¢. Thoracis tergum brunneo-piceum. 
Alz vitrine, nervis testaceis. Pedum antici fusco-picei, 
Juncturis pallidis ; posteriores lurido-straminei. Abdomen 
supra piceum, apicibus seementorum obscuris: “ venter 
rubiginosus” (Walk.). Sets bases versus sub-fuligi- 
nose. 
Long..corp. ¢ 10:5, al. 12 mm. 
Hab.—Incog. (? United States.) 
Genus HeEpraGenia. 
(Ala antica, Pl. III. fig. 5.) 
Ephemera, p., Pod. 1761; Baetis (A), Curt. 1834 (nec 
Leach, 1815) ; Heptagenia, Walsh, 1863 ; Hedyurus, Etn. 
1868. 
Nympha agile reptans, laminis branchialibus utrinque 
septem ; laminz simplices integree, fasciculis e radicibus 
singulis filamentorum branchialium. Femora late com- 
pressa, ciliata. Caput late depressum: labrum induplica- 
tum, transversum, obtuse triangulare, apice emarginato. 
Palpi maxillares bi-articulati: maxillarum superiores lami- 
nares, intus ciliate, antice (7. e., apud apices) pectinatz, 
palpis tenuibus ; inferiores palpis robustis ultimis arti- 
culorum bifidis, dimidiis imbricatis. Labium ovale mi- 
nutum, palpis inarticulatis, brevissimis, ob-ovatis. 
Subimago in habitfi Siphlwro admodum similis est. 
Imago. Alz quatuor: setaruam media caret: oculi 
maris simplices. Tarsorum posteriores quinque-articulati ; 
articulorum secundus, tertius, et quartus graduatim de- 
crescentes: ungues dissimiles. TF orcipis maris artus tri- 
articulati, proximis articulorum longissimis, ex apice pro- 
cessus Ventralis procedentes. Ovivalvulam et processum 
ventralem penultimi segmentorum femina habet. 
The species frequent streams and rivers in the Pale- 
arctic and Nearctic regions, the Andes, and the Malay 
Archipelago. 
