The Chonaphini 149 



margin indented. Acropodite long, slender, and aciciular, demarcated 

 from prefemur by strong constriction, bending anteriad basally, sublinear 

 for most of length, curving broadly distad, about 3/4 as long as prefemoral 

 process. Prostatic groove arising in pit in prefemur, running down 

 medial side of latter and curving onto lateral side of acropodite, curving 

 around latter and continuing to terminal opening. 



Cyphopod aperture long and narrow, encircling 2nd legs, sides 

 and caudal margin elevated above metazonal surface, more so medial- 

 ly. Cyphopods in situ with valves oriented transversely in aperture, 

 common surface visible in opening. Valves moderate-size, moderately 

 hirsute, without marginal extensions and central depression. Receptacle 

 moderate-size, ventrally hirsute, located on dorsomedial side of valves, 

 not alate and cupped around latter. Operculum large, located on dorso- 

 lateral side of valves, with long apical hairs. 



Distribution — Occurring in four segregated areas east of the Central 

 Plains including parts of Minnesota and Wisconsin; the lower peninsula 

 of Michigan, northwestern Ohio, and Indiana; one site in eastern Ohio; 

 and parts of Maryland, West Virginia, and Virginia. 



Species — One. 



Remarks — The only tribal component east of the Plains, Semionellus 

 is evidence of prior faunal linkage through the gap of some 1,053 mi 

 (1,684 km) in the northcentral United States. The Black Hills in western 

 South Dakota, an island of forested mountains in the midst of intervening 

 grasslands, is a plausible site for an undiscovered, relict, chonaphine 

 population that might bridge anatomical gaps between Semionellus 

 and Chonaphe. However, my field trip there in May 1986 produced 

 only parajulids and introduced species, and disclosed no xystodesmids, 

 possibly because of unseasonably cold weather (Shelley 1990). Hardwood- 

 fir environments in this area, particularly in Spearfish Canyon, the 

 north slope of Mount Harney, and the Iron Creek drainage above the 

 Needles Section of Custer State Park, should be reinvestigated in 

 warmer weather to ensure that the Black Hills do not harbor xystodesmids. 

 Inselberg ranges in Montana east of the Continental Divide like the 

 Big and Little Belt Mountains and the Absaroka and Bighorn Ranges 

 are other plausible areas for undiscovered chonaphines that would be 

 remnants of the ancient faunal connection. 



Semionellus placidus (Wood) 



Figs. 27-32 



Polydesmus (Leptodesmus) placidus Wood, 1864:9; 1865:225, fig. 56. 

 Polydesmus (Leptodesmus) floridus, var.? Wood, 1864:9; 1865:226. 



