Isoperla denningi Jewett

(Figs. 5 a-d)

Isoperla denningi Jewett 1955 .

Holotype ♂, California, Los Angeles County, 4 mi W Tanbark Flat.

Male. Aedeagus: sclerotized posterior process present; body with two posterobasal lobes, one large posteroapical lobe, and one dorsolateral pair of rounded lobes (Fig. 5a); sclerotized process length <0.5 mm, recurved and rod-like, apex clavate in lateral view (Fig. 5a), bifurcate in posterior view, lateral apices short and rounded (Fig. 5b), and width of expanded apicolateral lobes 0.09-0.10 mm. Abdominal terga 8-9, 9, 9-10: without stout spinulae or long stout setae. Posterolateral margins of at least abdominal segment 8 with scale-like setae clustered in brushes of several setae. Paraprocts: curved dorsally, length if straightened subequal to combined first and second cercal segments, tapering gradually to blunt apices (Fig. 5c). Vesicle: pedunculate, length subequal to width, constricted near base with curved lateral margins, wider and rounded at apex (Fig. 5d).

Isoperla denningi is common in southwestern California, from Santa Barbara County south to San Diego County and occasionally coexists with I. acula, I. adunca and I. mormona (Sandberg 2011b) . It is most similar to the species in the I. sordida complex, specifically I. sordida Banks 1906 (Table 1), with discernible differences in aedeagal characters. Both species have four aedeagal lobes in lateral view, however I. denningi has a pair of dorsal lobes and I. sordida has only one. The sclerotized processes are somewhat similar; both are slightly bifurcate with short rounded apices. The difference is the plane in which these apices lie: for I. sordida, the apical plane is perpendicular to the body of the process, and for I. denningi, the apical plane is parallel with the sclerotized process body. Additionally, the widths of the bifurcate apices differ: 0.09-1.0 mm for I. denningi and 0.18-0.20 mm for I. sordida .

Additional Material Examined. CALIFORNIA, Riverside Co., San Juan Creek, 0.4 mi (0.6 km) N Lion Canyon Creek, 19/ V /2011, larvae (ABLC); San Diego Co., Devils Canyon Creek, above San Mateo Canyon Creek, 16/ V /2011, larvae (ABLC); King Creek, 1.1 mi (1.77 km) below Grove Drive, 30/ V /2012, larvae (ABLC); Santa Ysebel Creek, 2 mi (3.2 km) S Dan Price Creek, 29/ V /2011, larvae (ABLC); Juaquapin Creek, above Sweetwater River, 01/ VI /2011, larvae (ABLC).