The Chonaphini 153 



visible in opening. Valves (Fig. 32) relatively large, subequal, ventral 

 surfaces flat, without depression, margins not extended, moderately 

 hirsute. Receptacle moderately large, located at dorsomedial corner 

 of valves, not alate, not cupped around latter, with long hairs arising 

 from ventral surface. 



Variation — The only noteworthy gonopodal variation concerns 

 the degree of serration on the medial flanges, which can be more or 

 less than on the illustrated specimen and quite jagged on occasional 

 males, and the thickness of the distolateral ledge, whose margin is 

 thickened on some males and expanded slightly into a rim lying perpen- 

 dicular to the axis of the prefemoral process. On a few males the 

 acropodite lies closer to the stem of the prefemoral process, running 

 through the curvature of the second medial flange. Facial setae on a 

 male from Tucker Co., WV, are epicranial 2-2, interantennal absent, 

 subantennae 1-1, frontal 1-1, clypeal about 12-12, labral about 18-18, 

 merging with clypeal series and continuing for short distance along 

 genal border, about 4 setae per side. 



Ecology — I have collected S. placidus in West Virginia in deciduous 

 forests and cove habitats under moist leaves near water sources. 



Distribution — The only tribal representative occurring in the east, 

 S. placidus inhabits four segregated areas. The western population 

 traverses the Mississippi River in the Central Lowland Physiographic 

 Province from southeastern Minnesota to southeastern Wisconsin and 

 may not be contiguous, as linkage has not been demonstrated between 

 the samples taken along the Mississippi and those in southern and 

 eastern Wisconsin. The central population, also in the Central Lowlands, 

 extends from the central part of the lower peninsula of Michigan, 

 near the base of the "thumb," through western Ohio to western and 

 south central Indiana. The eastern population, located in the Appalachian 

 Plateau, Ridge and Valley, and Blue Ridge Physiographic Provinces, 

 ranges from western Maryland through eastern West Virginia, to western 

 Virginia, reaching its eastern periphery in Shenandoah National Park. 

 There is also a single record from southeastern Ohio along the Ohio 

 River. Approximate areas of the populations are 273 mi (437 km) 

 east/west and 45 mi (72 km) north/south for the western, 245 mi (392 

 km) east/west and 332 mi (531 km) north/south for the central, and 

 98 mi (157 km) east/west and 137 mi (219 km) north/south for the 

 eastern. The western and central populations are separated by around 

 156 mi (250 km), and the central and eastern populations are segregated 

 by about 234 mi (374 km); the southeastern Ohio record is intermediate 

 between the last two areas. No specimens have been encountered in 



