. Bulletin - United States National Museum. usetts Ave., NW, past WisconsinAve., A. Pizzini, Feb. 11, 1939; nest of ants, Fairland, Haverland, Oct. 24, 1935;Frederick Co.: artesian well on S side of Sugarloaf Mt., T. Ulke, Apr. 17, 1938;spring and stream near top of Sugarloaf Mt., W. H. Ball, Apr. 9 and 17, VIRGINIA.—Jefiferson Co.: spring on Blue Ridge Mountains E. of Kabletown,E. T. Wherry, March 23, 1930. Pennsylvania.—Adams-Franklin Co. line:open stream at Caledonia State Park, A. Pizzini, July 11, 1937. SUBTERRANEAN AMPHIPOD STYGONECTES 63 Diagnosis.—Differing only from *S. t. t
. Bulletin - United States National Museum. usetts Ave., NW, past WisconsinAve., A. Pizzini, Feb. 11, 1939; nest of ants, Fairland, Haverland, Oct. 24, 1935;Frederick Co.: artesian well on S side of Sugarloaf Mt., T. Ulke, Apr. 17, 1938;spring and stream near top of Sugarloaf Mt., W. H. Ball, Apr. 9 and 17, VIRGINIA.—Jefiferson Co.: spring on Blue Ridge Mountains E. of Kabletown,E. T. Wherry, March 23, 1930. Pennsylvania.—Adams-Franklin Co. line:open stream at Caledonia State Park, A. Pizzini, July 11, 1937. SUBTERRANEAN AMPHIPOD STYGONECTES 63 Diagnosis.—Differing only from *S. t. tenuis in the absence of coxalgills on pereopod 7 in both sexes and in the absence of sternal gills onpleonite 1 of the male. Largest males, mm; largest females, mm. Variation.— Pronounced sexual dimorphism in the structure ofthe male second antenna in S. tenuis has already been noted. Theregression line in figure 14 illustrates the allometric size relationshipbetween antennal lengths and standard body length in males, and. Figure 13.—Stygonedes tenuis potomacus, new subspecies. Male ( mm), Glencarlyn,Va.: a, lower lip; b,c, right and left mandibles; d, maxilla 1; e, lateral sternal gill;/,maxilla 2; g, maxilliped; h,i, uropods 1,2. Male ( mm), Burleith Woods, Wash-ington, :;, telson; k, uropod 3; /, terminal flagellar segments of antenna 2. 64 NATIONAL AIUSEUM BULLETIN 2 59 although this graph is based on data gathered from specimens assignedto S. t. potomacus, it can be readily applied to either subspecies. Assize increases, length of antenna 2 approaches the length of antenna 1,and in males between and mm both antennae become aboutequal in length. Males over mm in length, however, typically 2nd Antenna Xh- o•z hi 111 h- :z< 3 St Antenna X / X
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