SUBTERRANEAN AMPHIPOD STYGONECTES 51 



In populations with smaller individuals (viz., Wetzels Spring and 

 Chester Co.) the distoanterior lobe appears to be rather well developed 

 in males which are 8.00 mm and longer. On the other hand, in 

 populations with larger individuals (viz., Refton Cave), this lobe 

 is still rudimentary or poorly developed in males as long as 9.00 mm. 

 It has also been observed that the palmar margin notch does not 

 become well defined until males reach a length of at least 12.00 mm 

 and is only barely discernible in males which have reached 10.00 mm. 

 Therefore, unlike the pereopod lobe, the palmar margin notch is 

 well defined only in males belonging to popidations with significantly 

 larger size means. Finally, in both sexes, sexually mature animals 

 in populations with larger size means have more marginal setae on 

 coxal plates than those animals in populations with smaller size means. 



Some possible reasons for this apparent size phenomenon are 

 discussed elsewhere in this paper (see Evolution, p. 148). 



Type locality. — Wetzels Spring, Glover Archbold Parkway, 

 Washington, D.C. The type locality is a small spring opening in a 

 low bank and flowing into a creek that drains the park. According 

 to Andrew Pizzini (pers. comm.), most of the material collected 

 dming the 1930s was taken from under decaying leaves and in gravels 

 near the point of resurgence. Three topotypes (1 female and 2 

 juveniles) were collected from under wet leaves about three feet from 

 the water source during field work in May, 1965. 



Distribution and ecology. — The presently known range for 

 S. pizzinii extends from Fairfax Co., Va., and Frederick Co., Md., 

 northeastward to Chester and Lancaster Counties, Pa. A 60 mile 

 gap occurs in the range between Howard Co., Md., and Lancaster 

 County, but this may be due to lack of collections rather than absence 

 of populations. 



S. pizzinii is apparently restricted to mterstitial habitats in Pre- 

 cambrian crystalline rock and overlying mantle of the Piedmont 

 Upland and to mterstices, solution channels, and caves developed 

 in lower Paleozoic limestone and upper Precambrian crystalline rocks 

 in the vicinity of Lancaster, Pa. Collections made to date have 

 been from outlets of several springs and seeps, from two wells, and 

 from one cave. 



The general range of this species overlaps a sizeable part of the 

 range of S. tenuis potomacus, new subspecies, in addition to over- 

 lapping the southeastern extremity of the range of S. allegheniensis, 

 new species; however, only one authentic record of syntopy exists 

 between S. pizzinii and species of the tenuis group, this being a 

 collection from an artesian well on the south side of Sugarloaf Moun- 

 tain in Frederick Co., Md., made in April 1938. In contrast to the 

 relative abundance of S. t. potomacus in the vicmity of Washington, 



