8 



Fresh-water Biology 



KEY TO THE GENERA OF MAYFLY NYMPHS: EPHEMEROPTERA* 



1 — Mandibles with a tusk projecting forward and visible from above the head 2 



— Mandibles with no such tusk 9 



2 — Tusk flattened, blunt- tipped, and bare (certain Western) Paraleptophlebia 



— Tusk sharp pointed and more or less hairy 3 



3 — Fore tibiae longer than the hind ones 4 



— Fore tibiae shorter than the hind ones 5 



4 — Mandibular tusks hairy to their tips Euthyplocia 



— Mandibular tusks hairy only at their base Potamanthus 



5 — Front of head with an elevated process 6 



— Front of head rounded 9 



6 — Frontal process rounded 7 



— Frontal process bifid at the tip 8 



7 — Mandibular tusks serrate on the sides Ephoron 



— Mandibular tusks smooth on the sides Hexagenia 



8 — Mandibular tusks minutely toothed on the sides Pentagenia 



— Mandibular tusks smooth on the sides Ephemera 



9 — Head strongly depressed: eyes dorsal: gills plate like 10 



— Head not strongly depressed: eyes lateral: gills various 19 



10 — Gill plates simple, bare Arthroplea 



— Gill plates with clustered gill filaments at the base 11 



11— Tails 2 12 



—Tails 3 15 



12 — With a pair of small dorsal spines on each abdominal segment . Ironodes 



— With no such spines 13 



13 — With a middorsal hne of hairs on the abdomen Ironopsis 



— With no middorsal line of hairs on the abdomen 14 



14 — Gill plates of first and last pairs directed laterally Epeorus 



— Gill plates of first and last pairs convergent ventrally Iron 



15 — Gills of segment 7 reduced to tapered filaments .Stenonema 



— Gills of segment 7 flat like the other gills 19 



* A standard illustrated reference work for this order covering both adults and nymphs is The- Biology of 

 Mayflies by Needham, Traver and Hsu, 759 pages, 1937 (Comstock Publishing Co., Inc., price S7.50). 



Unfortunately there are a number of name changes required by the rule of priority, that the users of former 

 editions of this Guide will need to know about: 



Isonychia replaces Chirotonetes. 



Paraleptophlebia replaces Leptophlebia in part. 



Heptagenia replaces Ecdyonurus, and is itself replaced by Stenonema. There now appears to be general con- 

 currence and agreement in the use of EPHEMEROPTERA instead of EPHEMERIDA as the name of the 

 Order. 



(Continued on page 10) 



Genera Figs. 



Acroneuria (5) 



Alloperla (5) 



Atoperla (S) 



Capnia (13) 



Chloroperla 1,(5) 



Hydroperla 15 



Isogenus (5) 



Isoperla 4 



Kathroperla (8) 



Leuctra 6,14 



Nemoura 3,9 



PLATE 1. STONEFLY NYMPHS 



Length Distr. Waters Genera Figs. 



20 G lotic Neoperla (5) 



12 G lotic Paraperla 8 



8 W, C lotic Peltoperla 2 



5 N lotic Perla (5) 



6 G lotic Perlesta (S) 



17 G lotic PerUnella 7,(5) 



20 N, W lotic Perlodes (5) 



13 G lotic Pteronarcella.... 11,(5) 



18 NW lotic Pteronarcys (5) 



10 G lotic Taeniopteryx. .. 10,12 



11 G lotic 



