SUBTERRANEAN AMPHIPOD STYGONECTES 65 



have tlie second antennae longer than the first antennae, and in very 

 large males the former may appreciably exceed the latter in length as 

 shown. In the largest males examined (16.50 mm) the second 

 antennae were 27 percent longer than the first antennae. But only 

 two specimens were found which had attained this length; the majority 

 of males were much smaller and the largest otherwise was only 

 12.00 mm. 



Type locality. — Bog in Burleith Woods, Glover Archbold Park- 

 way, Washmgton, D.C. A small stream flowing through Burleith 

 Woods is fed by a mnnber of small subterranean seeps which either 

 flow directly into this creek or form "swamps" and bogs along the way 

 during wet weather. 



Distribution and ecology.— jS. t. potomacus occurs southeast of 

 the Susquehanna River and east of the Chesapeake Bay westward to 

 the Blue Ridge Mountains and southward to the vicinity of Rich- 

 mond, Va. The majority of collections have been made in the imme- 

 diate vicinity of metropolitan Washington, D.C. The Richmond 

 record is the only one south of Prince William Co., Va., and the range 

 gap between these two sites is about 75 miles. The westernmost 

 record is a spring on the Blue Ridge Mountains east of Kabletown, 

 W. Va. The northernmost record is Caledonia State Park in Penn- 

 sylvania. Localities in Ann Arundel Co., Md., are only eight miles 

 west of the Chesapeake Bay. 



Collections have been made from seeps, bogs, springs, and wells, 

 and on the basis of these data it can be assumed that this subspecies, 

 like S. t. tenuis, is an inhabitant of shallow subterranean waters which 

 occur in crevices and joints of crystalline rocks of the Piedmont and 

 in interstices of unconsolidated sands, gravels, and silts of the Coastal 

 Plain. The largest number of collections have been made during 

 sprmg months (Feb. to May), thus possibly indicating that there is 

 either a seasonal migration to the surface or that animals are washed 

 out of underground habitats by later winter and early spring flooding. 

 The possibility, however, that both of these factors might be influen- 

 tial cannot be ruled out. S. t. potomacus has been taken syntopically 

 with ;S'. pizzinii from an artesian well in Frederick Co., Md., with 

 S. hayi from a small spring in the Zoological Park in Washington, 

 D.C, and occasionally with Crangonyx shoemakeri (Hubricht and 

 Mackin) from springs and seeps in the Washington, D.C. area. 



Collections are available for all months of the year but only those 

 made during March, April, May, and June contained ovigerous 

 females. Egg production in 24 females ranging m size from 5.55 to 

 9.00 mm (Mean = 6.90, S.D. = 1.11) is summarized as follows: 

 N=24, Mean=8.42, S.D.=2.21, C.V. =26.20%. Size of young 

 in the brood pouch =2.00 mm. 



