SUBTERRANEAN AMPHIPOD STYGONECTES 129 



even where landscapes are not particularly rugged. But on the basis 

 of the wide ranges of several contemporary species of Stygonectes (e.g., 

 S. tenuis, S. aUegheniensis, and S. alahamensis) , all of which to some 

 extent range over mildly rugged topography, one is compelled to 

 admit that given a proper terrain and geological horizon, certain 

 species of this genus apparently only recently possessed or still possess 

 rather well-developed abilities of dispersal. In accordance with pene- 

 planation major rivers wovild have flowed rather slowly and developed 

 broad flood plains. Loosely consolidated, flood plain alluvium might 

 easily be imagined to have pro^dded ample interstitial habitats for 

 colonization by stygonectids. Inland migration through interstices 

 developed along flood plains of major rivers may well have been the 

 most promising and most direct route into the central Appalachians 

 and the central Ozarks, assuming that the ancestral stock was already 

 phreatobitic. 



It is perhaps instructive to draw a zoogeographic parallel between 

 Stygonectes and subterranean cirolanid isopods. Two species of this 

 predommately marine group occm* in North American fresh waters — 

 Cirolanides texensis Benedict and Antrolana lira Bowman. The for- 

 mer species is rather widely spread throughout the subterranean 

 waters of central Texas, and in several localities of this area it is 

 associated with species of Stygonectes. The latter species is known 

 only from Madison Cave in Augusta Co., Va., a locality situated not 

 many miles from the range limits of tlu'ee species of Stygonectes. 

 Bowman (1964) considers these cirolanids as having resulted from 

 fresh-water invasion by ancestral stock during an earlier period of 

 embayment. He found no major problem in explaining the occur- 

 rence of C. texensis in central Texas, since this species inhabits an 

 area that was inundated by shaUow sea waters dm'ing the Upper 

 Cretaceous and was situated very close to marine waters again during 

 an extended period of the Cenozoic; however, the presence of A. lira 

 in the central Appalachians is much more difficult to explain, and 

 while Bowman (1964) presented several theories to explain its occur- 

 rence there, he conceded that invasion from the Atlantic coastal area 

 would have been the most probable route. An approximate time for 

 such an invasion was not clearly hypothesized, but I can see no reason 

 why an ancestral progenitor of A. lira could not have migrated to the 

 central Appalachians in a manner similar to that postulated for 

 ancestral Stygonectes. 



In summary, the foregoing theory postulates a series of fresh-water 

 invasions by ancestral, marine stygonectid stock beginning early in 

 the Cenozoic, or even in the Upper Cretaceous, and continuing for an 

 undetermined length of time. Ancestral stock was probably already 

 living in shallow coastal waters and perhaps in marine interstitial 



