464 BULLETIN" 15 8, UNITED STATES NATIONAL MUSEUM 



second maxilla club-shaped, armed at its distal end with a row of 

 stout spines; terminal claw with five longitudinal rows of spines. 

 Total length, 4.5-5 mm. 



Male. — Carapace elliptical, one-third the body length ; second seg- 

 ment the same width as the carapace, third and fourth segments 

 narrower; fifth segment narrower than fourth and only one-fourth 

 as long. Genital segment as wide as fourth segment and as long as 

 wide, with strongly convex sides. Abdomen 4-segmented, the two 

 basal longer than the two terminal segments, their lateral margins 

 convex; caudal rami broad, longer than the last two abdominal 

 segments combined, each tipped with three plumose setae. Total 

 length, 2-2.25 mm. 



Remarks. — This parasite clings to the very tips of the gill fila- 

 ments; when removed and placed in sea water, the male can swim 

 rather clumsily, while tlie female is helpless. 



NEMESIS PALLIDA, new species 



Plate 33, h-p 



Occurrence. — Both sexes have been found in abundance on the 

 gills of the following large sharks captured in the fish nets on 

 Marthas Vineyard: The thresher shark {VuJpecula iria^'ina) in 

 August, 1922, 1923, and 1925; the brown shark {C archarhinus mil- 

 herti) in July and August, 1923; the sand shark {Carcharias taurus) 

 in July, 1923; the tiger shark {Galeocerd\o arcticus) in August, 1925; 

 the great white shark {GaTcharodon, carcharlas) in July, 1924, and 

 August, 1925; the dusky shark {C archarhinus ohscw'us) in August, 

 1925. 



One female from the thresher shark with attached male is made 

 the species holotype, with U.S.N.M. No. 56632. 



Color. — Body pale yellowish white, contents of digestive tract 

 showing as an indistinct dark streak through the center of the body ; 

 egg strings brown. 



Female. — Carapace elliptical, longer than wide and evenly 

 rounded ; second and third segments a half wider than the carapace, 

 the second segment with smooth sides; fourth segment a little nar- 

 rower than the third. The plates covering the dorsal surfaces of 

 these three segments extend around the sides of the segments, but 

 the ends do not stand out free from the ventral surface, as in 

 atlantica and lamna. Instead the segment itself forms a thick pad, 

 and the plate simply covers the outside surface of the pad. The 

 fifth segment is much narrower than the fourth, with a 3-lobed 

 posterior margin, the middle lobe much wider than the lateral ones. 

 The dorsal plate on this fifth segment does not reach the lateral 

 margins, but leaves a free border on either side; there is also a 



