522 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.52. 



lar to those of diadema. These are characterized by the very large 

 swollen head of the penis and by the tbin sheU-hke anterior hamules. 

 Figure 143 shows the eggs of dorsalis drawn to the same scale as the 

 abdomiDal segments 9 and 10, figure 142. Figures 137, diadema, and 

 142, dorsalis, show the ovipositors of the females. The ovipositor con- 

 sists of a large ventral ovipositor proper wliich arises from the eighthseg- 

 mcnt and in thenymph is divided longitudinally. Tins may bo homolo- 

 gous to the ovipositor in the Aeshninae. In the concave dorsal sur- 

 face of this lie a pair of slender organs which in the nymph arise from 

 the ventral surface of segment 9. These in diadema do not extend 

 caudad beyond the apices of the appendages of segment 10, but in 

 dorsalis are much longer. These, because they arise from segment 9, 

 may be homologous to the genital valves of the aeshnine dragonflies, 

 though their position in the imagoes is just the reverse of these parts 

 in the Aeshninae. 



In color the two species are similar. The general color in tenerals is 

 chocolate brown which, in age, may become almost black. The mark- 

 ings are pure yellow. The frons in diadema is black mth a yeUow 

 oval on its dorsal surface while in dorsalis it is yellow with a dark band 

 across its anterior face. The markings of the abdomen in diadema 

 are characterized by the yellow oblique rings on segments 3 to 8, and 

 in dorsalis by the subcircular dorsal spots on segments 2 to 7. The 

 eyes in dorsalis are gray. (See figs. 133-134 and 138-139.) 



The n3niiphs of Cordulegaster are short-legged, slow-moving crea- 

 tures and are usually abundant in the streams of the Coast Mountains. 

 They occur with Octogomjyhus nymphs in the leafy trash of the eddies, 

 but are also found crawling slowly about over the bed of the stream. 

 Tlieir very slow and apparently cautious movements do not betray 

 them, and they carry with them further protection in the coat of long 

 hairs which collects dirt and on which flourishes a thick growth of 

 filamentous algae (see fig. 145, A). Because of this covering of dirt 

 and algae the nymph, though on an otherwise barren bottom, will 

 usually escape the closest scrutiny of the collector, for it does not 

 appear any different from a stick or stone covered with dirt and 

 aquatic growths.^ 



At emergence, which takes place in June (I found a single exuvia 

 May 31), the nymphs crawl from 1 to 5 feet up the trunk of the nearest 

 alder tree (see fig. 145, B). A male was reared in the laboratory, but 

 the hour of emergence was not ascertained. This species spends four 

 years in the egg and nymphal stages. 



The following table shows the four sizes of nymphs I collected on 

 Stevens Creek (Santa. Clara County, Cahfornia) during the past sum- 

 mer. The measurement used is the width of the head (eye to eye) ; 



1 On Mission Creek, Santa Barbara, California, I found nymphs of dorsalis buried in flocculent silt, as 

 is described by Dr. J. G. Needham (N. Y. State Mus. Bull. 47, 1901, p. 473) for the various eastern species 

 of this genus. 



