149 

 Smith and Pritchard: Odonata 



Na iads 



1. Dorsal setigerous margin of the median gill extending 

 beyond the middle of the gill 2 



— Dorsal setigerous margin of the median gill not extend- 

 ing beyond the middle of the gill (fig. 4:83a) 4 



2. Mental setae 3-5; lateral setae 6-7; marginal setae 5-9 



3 



— Mental setae 3; lateral setae 5; marginal setae 3 



prae varum 



3. Greatest width of middle gill about 1/4 of its length; 

 marginal setae 5-6 (fig. 4:83e) boreale 



— Greatest width of middle gill about 1/3 of its length; 

 marginal setae 6-9 (fig. 4:83/) cyathigerum 



4. Tracheae of caudal gills with numerous branches which 

 tend to curve; dorsal setigerous margin of middle gill 

 not extending to middle (fig. 4:836) 5 



— Tracheae of caudal gills with fewer and straighter 

 branches; dorsal setigerous margin of middle gill 

 extending to about middle (fig. 4:83a) clausum 



5. Lateral carina of segment 1 with a few spinose setae; 

 dorsal setigerous margin of middle gill extending about 

 three-sevenths of length; gills diffusely pigmented 

 (fig. 4:83c) carunculatum 



— Lateral carina of segment 1 without spinose setae; 

 dorsal setigerous margin of middle gill extending about 

 1/3 of length; gills with pigment only in small tracheae 

 (fig. 4:83c) civile 



Genus Ischnura Charpentier, 1840 



Ischnura males are black with greenish markings on 

 the thorax and blue markings caudally on the abdomen 

 (figs. 4:90a; 4:92). 



Females exhibit marked dichromatism (figs. 4:90; 

 4:91; 4:92). The homeochromatic form exhibits color 

 markings similar to that of the male, but it becomes 

 dull pruinose in later life. The heterochromatic female 

 is often the more common form of this sex, and it is 

 black with a more extensive, orange coloration. How- 

 ever, this form also becomes pruinose with age, the 

 pale markings becoming indistinct. 



Adults are found where there is an abundance of 

 aquatic vegetation in still water, but they may stray 

 into fields. Copulation usually takes place while 

 resting on plants, and the males usually leave the 

 females before oviposition. Eggs are laid singly in 

 the stems and leaves of aquatic plants. Naiads (fig. 

 4:93) occur among the vegetation of quiet waters of 

 lakes, ponds, swamps, and streams. 



Kennedy (1917, p. 500) writes concerning Ischnura 

 denticollis: "The habits of this species are in general 

 ischnuran but indicate greater feebleness. Early in 

 the morning it is found in the sedges and grasses 

 bordering the water but during the heat of the day it 

 spends the greater part of its time over the surface 

 of the water, usually seated on trash or aquatic 

 vegetation. 



"The females resorted to the little drain ditches 

 to oviposit; there the males in great numbers awaited 

 their coming. After a considerable time in copulation 

 seated on some grass stem, the female, still accom- 

 panied by the male, would fly to the surface of the 

 stream, preferably a quiet lateral pool, and commence 

 ovipositing. 



u The naiad of anna is not described. 



Fig. 4:87. Lateral views of male abdominal appendages of 

 Ischnura, a, barber i; b, aemorso; c, ramburii; d, gemina; e, 

 perparva; f, cervu/a; g, erraiica; h, denticollis (Celeste Green). 



"In ovipositing the male held the female by the 

 head. The pair would alight on floating vegetation, 

 in a horizontal position, and the female, would bend 

 her abdomen slightly and make usually one or two 

 incisions, after which she would raise the end of 

 her abdomen considerably above the horizontal and 

 wait in this position several seconds, when the pair 

 would fly to another straw and repeat the one or two 

 thrusts followed by the wait with the tip of the 

 female's abdomen in the air. This was kept up, b\ a 

 pair under observation, for twenty minutes. In no 

 place did they make more than one or two thrusts, 



Kennedy (1917) proposed the genus Celaenura for 

 Ischnura denticollis and /. gemina, and the generic 

 distinction is probably valid. However, Inter workers 

 have withheld the use of this name pending more 

 revisionary studies. 



Key to California Species 

 Males 



1. Mesothorax with dorsum solid black (fig. 4:92) 2 



— Mesothorax with pale spots or stripes on dorsum .... 3 



2. Ventral appendage slender and pointed, the dorsal 

 branch not projecting (fig. 4:87A) (Utah to California, 



