. Bulletin. Natural history; Natural history. 374 ILLINOIS NATURAL HISTORY SURVEY BULLETIN XX:IV PERLIDAE KEY TO GENERA CONT D. Median ocellus lacking or so poorly developed that only lateral ocelli are clearly visible, fig. 300; head therefore appearing to have but two ocelli. .3 Median ocellus well developed, fig. 301; head therefore clearly with three ocelli 4 Lateral ocelli close together, much closer to one another than each lateral ocellus is removed from compound eye. Forewing without crossveins in anal field and with many crossveins before subcosta, fig. 181. Ninth ventral abdominal se
. Bulletin. Natural history; Natural history. 374 ILLINOIS NATURAL HISTORY SURVEY BULLETIN XX:IV PERLIDAE KEY TO GENERA CONT D. Median ocellus lacking or so poorly developed that only lateral ocelli are clearly visible, fig. 300; head therefore appearing to have but two ocelli. .3 Median ocellus well developed, fig. 301; head therefore clearly with three ocelli 4 Lateral ocelli close together, much closer to one another than each lateral ocellus is removed from compound eye. Forewing without crossveins in anal field and with many crossveins before subcosta, fig. 181. Ninth ventral abdominal segment without a disklike structure in middle of posterior portion Neoperla, p. 381 Lateral ocelli far apart, at least as far removed from one another as each lateral ocellus is re- moved from compound eye. Forewing with crossveins in anal field and few if any cross- veins before subcosta, fig. 179. Ninth ventral abdominal segment with a disklike structure in middle of posterior portion .. .Atoperla, p. 377 Ninth ventral abdominal segment with a disklike structure in middle of posterior portion, fig. 302 7 Ninth ventral abdominal segment without a disklike structure in middle of posterior ..5 Fifth dorsal abdominal segment much different from preceding segments, enlarged and pro- longed backwards, figs. 206, 207. Tenth dorsal abdominal segment divided in middle and with a pair of genital hooks directed forward, figs. 206, 207 6 Fifth dorsal abdominal segment similar to preceding segments. Tenth dorsal abdominal segment undivided and without genital hooks, fig. 202 Perlesta, p. 384 6. Genital hooks on tenth dorsal abdominal segment short, fig. 206 Togoperla, p. 412 Genital hooks on tenth dorsal abdominal segment very long, fig. 207. . Neophasganophora, p. 407 7. Forewings with few or no crossveins in costal cell and several crossveins be- tween first and second anal veins, fig. 180. Compound eyes set forward on side of head about their diameter distant from hind margin
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