Stonefly Species Sweltsa occidens (Sallflies)

Source: A Contribution To The Knowledge Of Sweltsa Exquisita (Frison) And Sweltsa Occidens (Frison) And Description Of A New Species Of Sweltsa From The Northern Rocky Mountains, U. Sweltsa A. (Plecoptera: Chloroperlidae)

Male. General color yellow in life, head with dark ocellar rings, pronotum yellow, but with dark lateral margins, black stripe running down terga 1 - 8, terminal mark on tergum 8 longer than wide and never divided. Tergum 9 lacking bare elevated process (Fig. 10). Epiproct erectile, elongate, in dorsal view, tapered to apex (Fig. 10); extreme apex bare, (Figs. 10 - 13), in lateral aspect, apex expanded ventrally, but generally flattened laterally (Figs. 12 & 13); dorsal and lateral surface of epiproct covered with dense pile of long appressed setae, extending to the epiproct base (Figs. 10 - 13), laterally, base bare (Fig. 12). Aedeagus tubular, constricted near upper 1/3, with two bulbous lobes, bearing two smaller apical projections (Figs. 14 & 15), more expanded apex with broad lobes and dorsal finger-like projection medially (Fig. 16), surface with comb-like setae arranged in interrupted rows, with patch of stronger setae located at base of constricted area (Figs. 16 & 17).

Female. Color and markings similar to male. Subgenital plate subtriangular and not covering all of sternum 9, apex more narrowly rounded, often exhibiting a shallow emarginate area at the tip, but the posterior margin is usually entire (Fig. 27) for Sweltsa durfeei.