The Chonaphini 113 



are no faunal linkages between the western Nearctic and Meso-America, 

 and the Chonaphini is the only common tribe between the West and 

 East. 



The Chonaphini occurs primarily in the western United States 

 and Vancouver Island, Canada (Fig. 1), where there are currently 5 

 genera and 11 nominal species (Shelley 1990, 1993^). West of the 

 Columbia Plateau, Tubaphe levii Causey inhabits rainforests of the 

 Olympic Mountains and Vancouver Island, and Chonaphe armata 

 (Harger) and C. remissa Chamberlin occur sporadically in western 

 Oregon and Washington, respectively (Shelley 1990, 19936). In the 

 western interior, the tribe is represented by Montaphe elrodi (Chamberlin), 

 the dominant xystodesmid from eastern Washington to western Montana, 

 C. armata, also occurring sporadically in western Montana, northern 

 Idaho, and northeastern Oregon and Washington, and Metaxycheir 

 prolata Buckett and Gardner, localized in Latah and Benewah counties, 

 Idaho, and the adjacent eastern periphery of Whitman County, Washington 

 (Buckett and Gardner 1969, Shelley 1990). I place three additional 

 nominal species — C. cygneia and patriotica, both authored by Chamberlin, 

 and C. serratus Loomis and Schmitt — in synonymy under C. armata. 

 East of the Central Plains, the Chonaphini is represented by Semionellus 

 placidus (Wood), which occurs primarily in three general areas: from 

 southeastern Minnesota to eastern Wisconsin, from central Michigan 

 to western Indiana, and from western Maryland to westcentral Virginia 

 (Shelley 1990). 



In addition to its biogeographic significance as a trans-Nearctic 

 taxon, the Chonaphini is unique in that it reverses the basic anatomical 

 pattern of the family. In other xystodesmid tribes, the gonopodal acropo- 

 dite possesses most diagnostic features and is often elaborate, whereas 

 the prefemoral process is variable but generally simple and with little 

 taxonomic utility. In the Chonaphini, however, the acropodite is typical- 

 ly the simple structure, while the prefemoral process is usually larger 

 and often elaborate, displaying flanges and other projections from its 

 stem. The prefemoral process is thus the dominant feature of most 

 chonaphine gonopods and exhibits most taxonomic characters. Indeed, 

 the acropodite, usually a curved acicular to narrowly blade-like projection, 

 is so thin and fragile in most species that it is easily broken during 

 dissection, so care is needed to remove a gonopod with this structure 

 intact. 



With these basic attributes of the prefemoral process and acropodite, 

 the Chonaphini seems at first to be a coherent assemblage whose 

 study is comparatively straightforward, but there are undescribed forms 

 that depart from this pattern, cannot be accommodated by other western 



