ENALLAGMA 313 
black, with occasional pale spots around the ocelli. Antennae are en- 
tirely black, or black with the two basal joints pale. Pale postocular 
spots are always present, in some species small and entirely surrounded 
by the black of the head, in others large and united with each other by 
way of the pale occipital stripe on the rear of the head, or united with 
the pale of the rear of the head, that is, the postgenal and occipital 
region, in still other species they are very thin and linear. The pro- 
thorax is predominantly black, with superimposed pale areas and spots. 
Certain species have a pair of dorsal pits on the prothorax in the fe- 
males. The thorax is always predominantly pale, never metallic green, 
with a black middorsa]l and humeral stripe of varying width and extent, 
and usually reduced basal black markings on the second and third 
lateral sutures. Mp arises between the fourth and sixth, usually the 
fourth and fifth, postnodal cross vein in the fore wings, and between the 
third and fifth in the hind wings. The legs always have the front row 
of setae on the tibia less than twice as long as the spaces between their 
bases. The coloration of the abdomen varies greatly and is used for the 
determination of species. The females all have a ventral spine on the 
apical margin of abdominal segment eight. The appendages of the 
malevary greatly also, and are the final criteria for specific deter- 
mination. 
The nymphs live in tangled submerged vegetation, and are among the 
most numerous of the predatory hordes in such places, living on other 
insect larva, small crustaceans, etc. They are eaten by larger aquatic 
insects and vertebrates, especially the shallow-water fish. 
Of the thirty-eight described species of North American adults, the 
nymphs of only eighteen are known, and only fourteen have been ade- 
quately described. Their identification is difficult and it is quite im- 
possible to write a satisfactory key for their separation in the light of 
our present incomplete knowledge of them. In general, the nymph of 
Enallagma is slender, nearly smooth, with the head a third wider than 
the succeeding parts of the body. Antennae long slender, six or seven 
jointed, the segments generally increasing in length to the third, de- 
creasing thereafter to the tip. Labium slender with a prominant median 
lobe, which has a row of 3-9 setae on the lateral margins in addition to 
the mental setae, numbering from 2-4 on a side. Lateral setae 4-6. 
Legs usually smooth with a preapical brown ring on the femora. The 
abdomen cylindric, each segment with lateral keels, well or poorly de- 
veloped, and carrying in some species clumps or rows of heavy setae. 
The gills vary greatly as to size and pigmentation, but do not possess 
the long tapering points of Ischnura and Anomalagrion. 
