56 Rowland M. Shelley 



anatomical modifications are visibly striking. However, while examining 

 museum collections, I discovered individuals from epigean populations 

 that lack these features; the relative proportions of their podomeres 

 and antennomeres are similar to those of T. spinicaudus and T posticus. 

 These surface forms are geographically proximate to, and clearly con- 

 specific with, cave populations of T. phanus, which is consequently 

 a highly variable species demonstrating a level of genetic plasticity 

 that is not apparent in other Nearctic cryptopids. Occasional specimens 

 of Scolopocryptops sexspinosus (Say) have been discovered in caves, 

 but they are identical anatomically to epigean individuals and are not 

 modified by the subterranean environment. 



This study of the Plutoniuminae, the first monographic treatment 

 of a supra-generic chilopod taxon since Attems' (1930) ordinal treatise 

 on the Scolopendromorpha, derives from an ongoing survey of North 

 American scolopendromorphs. The discovery of the widespread, anatomi- 

 cally variable southwestern population of T. posticus and the resultant 

 deduction of the correct binomial for T. californiensis (Shelley 1990a) 

 focused attention on Theatops and led to the deletions of T. spinicaudus 

 from Hawaii, Mexico, and Canada (Shelley 1990a, 1991). These works 

 indicated that T. erythrocephalus should be examined in its proper 

 context, along with the American congeners, and that P. zwierleini 

 should be included to consolidate knowledge of the subfamily. The 

 Plutoniuminae is thus one of the few chilopod family-group taxa that 

 is amenable to a modern, all-inclusive treatment, because of its limited 

 composition and occurrence in only two biogeographic regions. Because 

 of the difference in the number of spiracles, Verhoeff (1906, 1907) 

 and Schileyko (1992, 1996) believed that separate families were required 

 for Plutonium and Theatops, and Schileyko (1996) even suggested that 

 Plutonium deserved a separate superfamily as an "absolutely different 

 group." However, most authors, including myself, subscribe to the system 

 originated by Attems (1930), in which Theatops and Plutonium are 

 assigned to the same subfamily. Such features as the depigmented patches 

 in the ocellar positions, the elongated ultimate tergite, and the heavily 

 sclerotized, forcipulate caudal legs constitute strong synapomorphies 

 that unite Theatops and Plutonium in a monophyletic group. Although 

 unique to the Scolopendromorpha, the autapomorphic 19 pairs of spiracles 

 in Plutonium is only a generic feature; using it as the basis for a 

 separate family or superfamily overemphasizes the character's signifi- 

 cance in relation to the several attributes that are shared with Theatops, 

 which indicate common ancestry. Consequently, I believe that the present 

 concept of the Plutoniuminae represents a natural assemblage of related 

 taxa. 



