(Figs. 12, 24, 30, 36, 42, 48, 60, 70, 84 a-b, Table 1)

Distribution. Pacific Northwest; Coastal and Cascade Mountains of Washington, British Columbia.

Material examined. Washington: Pierce Co., Fryingpan Creek, Sunrise Road, Mount Rainier National Park, 13-VII-2003, B. Kondratieff, J. Schmidt, 1♂, 2♀ larvae; 14-VII-2004, B. Kondratieff, 5♀; Nisqually River, Longmire, Mount Rainier National Park, 28-V-1997, B. Kondratieff, 2♂, 1♀, 2♂ larvae; White River, Hwy. 410, Mount Rainier National Park, B. Kondratieff, 8♂, 1♀, 3♂ larvae, 3♀ larvae, 1♂ exuvium, 2♀ exuviae; 20-VI-2003, B. Kondratieff, R. Zuellig, J. Schmidt, 2♀.

Characters. Head capsule width ♂ 3.06-3.30mm, ♀ 3.90-4.62mm; pronotal width ♂ 2.88-3.12mm, ♀ 3.36- 4.08mm; body length ♂ 18.3-19.5mm, ♀ 19.5-24.0mm (Table 1). Color and pigmentation (Figs. 12, 24, 30, 36, 42, 48), lacinia, and dorsomesal band of erect silky white hairs typical of genus. Wingpads of ♂ and ♀ macropterous. Gill number and arrangement typical of genus (Fig. 70). Submental gill length ♂ 0.12- 0.42mm, ♀ 0.36-0.45mm; anterior supracoxal gill length ♂ 0.27-0.42mm, ♀ 0.36mm (Table 1). Legs (Fig. 30) with setation typical of genus as described by Stewart & Stark (2002).Y-arms of mesosternum (Fig. 36) typical of genus. Cercal segments ♂ 24-26 (Table 1), with setation typical of genus. Developing membranous, windsocklike process of male epiproct (Figs. 42, 48, 70) evident in late instar individuals, and pointed posteroventrally in lateral view (Fig. 79).Developing female subgenital plate of 8 th sternum (Figs. 49, 84a, b) shallowly notched mesally.

Comments. The generic characters proposed by Stewart & Stark (2002), based solely on M. signata, are reaffirmed in this species, and color and pigmentation fit the generic pattern illustrated herein for M. signata. The measured gill lengths and shapes were greatly variable in this species (Table 1), and otherwise similar to M. signata.