10 U.S. NATIONAL MUSEUM BULLETIN 259 



apply the term troglobite to a large number of aquatic, subterranean 

 species. This, of course, depends to some extent on how narrowly 

 one prefers to delimit and define the biotope in question, since many 

 "troglobitic species" of gammarid amphipods, as well as asellid 

 isopods, occur not infrequently (although possibly accidentally) in 

 surface seeps and springs. It is perhaps significant to point out that 

 many species of Stygonectes are known almost exclusively from 

 "epigean habitats" such as seeps and springs; others are known 

 from seeps and springs as well as from caves, and still other species 

 are known only from caves. I have, however, generally interpreted 

 those species found most often in seeps and springs as being repre- 

 sentative of a shallow ground-water fauna, which from time to time 

 occurs on the surface through accidents of flooding or as the result 

 of periodic fluctuation of the ground-water table. It is doubtful 

 whether any of these species can live permanently in even such 

 secluded epigean habitats as under leaves and gravels in springs, but 

 it must be emphasized that the precise biotope for a large number 

 of subterranean amphipod species has not yet been determined. 



European workers, well experienced by many years of observation 

 on the seemingly erratic and paradoxical ecology of the widespread 

 subterranean amphipod Niphargus, have developed an extensive 

 terminology to cover the many biotopes inhabited by their contmental, 

 subterranean fauna. The study of subterranean, aquatic biology in 

 the United States, however, has been slow to develop, and while the 

 European literature on this subject is profuse, American hterature 

 is in marked contrast, sparse. Husson (1960) has listed a variety of 

 biotopes inhabited by various species of Niphargus in European 

 subterranean waters. An even more thorough delimitation and 

 discussion of the kinds of biotopes occupied by Niphargus has been 

 given by Bouillon (1964). As indicated in the lists of Husson and 

 Bouillon, there appear to be many ecological parallels between species 

 of Niphargus and Stygonectes. 



Vandel (1964) has presented an inclusive, annotated list of all 

 subterranean biotopes presently recognized by European biospele- 

 ologists; but he has pointed out further, and correctly, that it is not 

 always possible to draw a clear-cut distinction between one ground- 

 water biotope and another. The French have made extensive use of 

 the term nappe phreatique in reference to the upper layer of ground 

 water. Vandel (1964) has included this ecological zone as one of six 

 or seven different types of subterranean biotopes under the broader 

 mUieu interstitiel or interstitial environment. Of further note is the 

 recent work of Motas and Serban (1965) on phreatobiology. These 

 workers have introduced the term "phreatobios" to designate the 

 fauna which inhabits the nappe phreatique. 



