12 



Fresh-water Biology 



{Continued from page 10) 



36 — Maxillary palpus 2-jointed: tarsi longer than tibiae Metretopus 



— Maxillary palpus 3-jointed : tarsi at least as long as the tibiae Siphloplecton 



37 — Posterolateral angles of the terminal abdominal segments prolonged into thin flat 



lateral spines 38 



— These angles not greatly prolonged, hardly more than acute 41 



38 — Fore legs conspicuously fringed within by a double row of long hairs: Gills on base of 



maxillae Isonychia 



— No such hair fringes, and no gills on maxillae 39 



39 — Gill plates single on abdominal segments 1 to 7 40 



— Gill plates double on some of these segments . Siphlonurus 



40 — Abdominal segments 5 to 9 very wide, onisciform SIphlonlsca 



— Abdominal segments 5 to 9 normal 42 



41 — Maxillar}^ palpus somewhat pincer-shaped at tip, and end of lacinia beset with simple 



spines Parameletus 



— Maxillary palpus normal at tip, and end of lacinia beset with pectinate spines 



Ameletus 



42 — Gill plates folded double on some of the anterior abdominal segments 43 



— Gill plates all single 45 



43 — Tracheae of the gill plates pinnately branched: two pairs of wing buds Cloeon 



— These tracheae palmately branched: hind wing buds lacking 44 



44 — Gill flap folded over ventral surface: maxillary palpus 2-jointed Callibaetis 



— Gill flap folded over dorsal surface of the gill plate: maxillary palpus 3-jointed 



Centroptilum 



45— Tails 2 _ 46 



— Tails 3 (except in the Western Baetis bicaudatus) 47 



46 — Hind wing buds present (very minute) Heterocloeon 



— Hind wing buds lacking Pseudocloeon 



47 — Middle tail shorter than the others (except in B. tricaudatus) Baetis 



— Middle tail as long as the others: last joint of labial palpus widely dilated 48 



48 — Hind wing buds present Centroptilum 



— Hind wing buds absent: gill tracheae branched to one side Neocloeon 



Genera Figs. 



Ameletus 4 



Ametropus (4) 



Baetis (4) 



Baetisca 10 



Brachycercus. . . (1) 



Blasturus 3, (4) 



Caenis 1 



Callibaetis (4) 



Centroptilum ... (4) 



Chloeon (4) 



Choroterpes 9 (4) 



Cynigma (5, 12) 



Cynigmula (5, 12) 



Epeorus 8 



EphemereUa .... 6 



Habrophlebia ... 1 1 (4) 

 Habrophlebiodes. (4) 



Heptagenia 5 



PLATE 3. MAYFLY NYMPHS 



Length Distr. Waters Genera Figs. 



9 G both Heterocloeon.... (4) 



15-17 SW lotic Iron (8) 



6 G lotic Ironodes (8) 



10 E, C lotic Ironopsis (8) 



5-7 6 static Leptophlebia . , . . 7(4) 



9 E both Metretopus (4) 



3 G static Oreianthus (1) 



9 G static Paraleptophlebia 7(4) 



4 G static Parameletus.... (4) 

 8 G static Pseudocloeon ... (4) 



7 G lotic Rhithrogena . . . . (5) 

 8-9 NW lotic Siphlonisca (4) 



7 N, W lotic Siphloplecton ... (4) 



8 G lotic Siphlonurus 2(4) 



8-15 G both Stenonema 5 



5 E lotic Thraulus (4) 



6 E static Tricorythodes. . . (1) 

 10 G lotic 



