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Terms

1.         Lacinia with a single, sometimes short tooth (Fig.1.1). . . . . . . . . . . . . . . . . . . . . . 2

            Lacinia with two teeth (Fig.1.2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.         Lacinial tooth projecting clearly beyond primary setae. Small to medium-sized                         streams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isoperla nana

            Lacinial tooth short, sometimes absent or scarcely projecting primary setae. Small             streams (Fig.1.4). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isoperla decepta

3.         Body of lacinia subequal in length to longest tooth (Fig.1.5). . . . . . Isoperla burksi

            Body of lacinia distinctly longer than longest tooth. . . . . . . . . . . . . . . . . . . . . . . . 4

4.         Abdominal terga without distinct longitudinal dark stripes. . . . . . . . . . . . . . . . . . . . 5

            Abdominal terga with distinct longitudinal dark stripes. . . . . . . . . . . . . . . . . . . . . . 7

5.         Abdominal terga dark, often patterened with pale spots but transverse banding, if             present, consisting of two dark bands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

            Abdominal terga each with a single dark transverse band along posterior margin;             lacinia with approximaately 6 major setae set near base of second tooth; abdominal             tergum 10 predominantly pale. . . . . . . . . . . . . . . . . . . . . . . . . . . Isoperla signata

6.         Median and lateral dark abdominal stripes similar in width and pigment intensity on             terga 7 to 8. Darkest pigment on head not usually connected anterior to median             ocellus, or behind lateral ocelli; abdominal terga white adjacent to dark stripes; lacinial             setal row extending to midlenth of inner margin. . . . . . . . . . Isoperla transmarina

            Dark median stripe absent, or either wider, narrower, or more poorly defined than             lateral stripes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

7.         Dark median abdominal stripe wider and more prominent than lateral stripes;                         abdominal terga dark on either side of median stripe and bearing small freckle-like             spots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isoperla dicala

            Dark median abdominal stripe narrower and often less prominent than lateral stripes;             abdomiinal terga pale on either side of median stripe. . . . . . . . . . . . . . . . . . . . . . . 8

8.         Ocellar triangle open across posterior margin; pale areas on posterior abdominal             terga small; generally smaller than dark lateral pigment; lacinial setae row extends             along much of inner margin. . . . . . . . . . . . . . . . . . . . . . . . . . . .Isoperla bilineata

            Ocellar triangle usually closed on posterior margin; dark lateral abdominal stripes             prominent but not as wide as pale areas on terga; laciinial setal row extending along             less than half the inner lacinial margin. . . . . . . . . . . . . . . . . . Isoperla holochlora

I. montana bidentate with row of hair tufts below.

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