. Bulletin - New York State Museum. Science. AQUATIC INSECTS IN NEW YORK STATE 231 tions of imagos. I present a key based chiefly on the form of the male appendages, which will be sufficient, I trust, for the deter- mination of species. Of these nine species I have reared five. I regret to acknowledge, after prolonged study of them, that I find them well nigh indistinguishable specifically. Aside from slight and inconstant differences in size and a few very minor structural characters, they are all alike! I will give therefore a general description of them and supplement it with a tabular stat
. Bulletin - New York State Museum. Science. AQUATIC INSECTS IN NEW YORK STATE 231 tions of imagos. I present a key based chiefly on the form of the male appendages, which will be sufficient, I trust, for the deter- mination of species. Of these nine species I have reared five. I regret to acknowledge, after prolonged study of them, that I find them well nigh indistinguishable specifically. Aside from slight and inconstant differences in size and a few very minor structural characters, they are all alike! I will give therefore a general description of them and supplement it with a tabular statement of such differences as I have thus far been able to discover between them. Nymph. The nymph of Lestes is exceedingly long and slender, with wide head, deep thorax and slender, cylindiic ab-. Fig\ 7 Nymph of Lestes rectangularis; A, gills, more enlarged domen, bearing linear-oblong gill plates. Head twice as wide as long, only moderately prominent at the front; eyes prominent, rounded, directed somewhat anteriorly; hind angles low, well rounded, with a shallow wide notch between them on the hind margin; antennae longer than the head, with the segments in- creasing in length to the third, and decreasing thereafter to the tip, seven-jointed. Labium [, ] long and exceedingly slender, the hinge reaching as far posteriorly as the hind legs, 1 but dependent, and not closely applied to the ventral surface of the body; mentum linear to the suddenly dilated, and spoon- shaped tip; median lobe moderately prominent, with a closed median cleft which extends as far proximally as the level of the bases of the lateral lobes; mental setae well developed; lateral lobe very complicated [see , ], bent almosl at a right angle just beyond its base, having a very large movable hook, be- yond the base of which the <lis<al portion is cleft into (wo parts, the inner one of which bears the end hook and the usual Inner series of teeth, these being very numerous, regular and
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