SUBTERRANEAN AMPHTPOD STYGONECTES 141 



feed ground water to the subterranean system that produces this 

 large spring, has not resulted in the discovery of additional amphipods 

 conspecific with S. pecki. 



S. dejectus, also an extremely rare species, is known only from two 

 specimens collected from Cascade Caverns, which is located less than 

 50 mUes west-northwest of Comal Springs. The underground drain- 

 age in the vicinity of this cave is believed to be extensive, but its 

 limits and exact points of resurgence are unknown (ReddeU, pers. 

 comm.). 



Taxonomically, S. dejectus and S. pecki have been assigned to the 

 same species subgroup (i.e., pecki subgroup). Morphologically, these 

 two species share close affinities, but whether or not they have been 

 derived directly from an immediate common ancestor is questionable. 

 Largely because of undiscovered males in both S. pecki and S. de- 

 jectus, the exact relationship of these species to those in the flagellatus 

 subgroup is not clear. Assuming little or no appreciable sexual 

 dimorphism, which is generally lacking in cavernicolous species of 

 this genus, the two major points of divergence between these two 

 subgroups appears to be the proportionately shorter pereopods and 

 antennae and the lack of lateral spines on the telson in both species 

 of the pecki subgroup. The reduction in all three of these characters 

 is strongly indicative of evolutionary modification and specialization, 

 and I am, therefore, inclined to regard the flagellatus subgroup as 

 the older of the two subgroups and, accordingly, morphologically 

 closer to ancestral stock for the entire species group. 



Species of the flagellatus subgroup, i.e., S. flagellatus and S. longipes, 

 are, like species of the pecki subgroup, rare and greatly restricted in 

 range. S. longipes is known only from three specimens taken from 

 a stream in the lower level of Cave Without-A-Name (Century 

 Caverns) in Kendall County. This cave is developed in the lower 

 Glen Rose limestone, and observations reveal that its extensive, 

 lower level stream resurges through the spring entrance of Dead Man's 

 Cave, which is located several thousand feet away (Craun, 1948; 

 Reddell, 1964a). The source of the stream in Cave Without-A-Name 

 is unknown, although Mitchell and Reddell (1965) suggested that 

 Cave Without-A-Name and Cascade Caverns, which are located about 

 sixteen miles apart, presumably share in a common water system. 

 To what extent S. longipes may be restricted to this particlar under- 

 ground stream system is debatable, but random collecting in other 

 caves of this area has not uncovered additional specimens of this 

 species. While Mitchell and Reddell's presumption appears to be 

 substantiated from evidence on the distribution of a subterranean 

 salamander (i.e., Eurycea latitans) it has not yet been borne out by 

 data obtained on the distribution of subterranean amphipods. 



