410 



BULLETIN" 15 8, UNITED STATES NATIONAL MUSEUM 



1. Abdomen 2-segmentecl, basal one-third as long as end segment; 



carapace as wide as long nordmanii (p. 411) 



Abdomen 1-segmented ; carapace distinctly longer than wide 2 



2. Fourth legs reaching beyond tips of caudal rami ; genital seg- 



ment not so wide as fourth segment hippoglossi (p. 412) 



Fourth legs scarcely reaching center of genital segment ; the lat- 

 ter wider than fourth segment 3 



3. Genital segment obovate, widest anteriorly ; spines on fourth 



legs flanged edwardsi (p. 412) 



Genital segment orbicular, widest at its center; spines on fourth 



legs not flanged thompsoni (p. 410) 



LEPEOPHTHEIRUS THOMPSONI Baird 



FiGUKH 257 



LepeoplitJieirus tliompsoni Baikd, The natural history of the British Ento- 

 mostraca, p. 278, pi. 33, fig. 2, 1850.— Wilson, Proc. U. S. Nat. Mus., vol. 

 28, p. 619, pi. 18, 1905. 



Occun^ence. — Both sexes found on outside surface of goosefish at 

 Woods Hole by Vinal Edwards in 1904. 



Distribution. — British seas (Baird, T. Scott, Bassett-Smith, 

 White) ; Mediterranean (Brian) ; Faroe IsLands (Hansen) ; Kattegat 



and North Sea (Kr0yer) ; Bohuslan 

 (Malm, Olsson) ; La JoUa, Calif. (Wil- 

 son). 



Color. — Body a uniform light yellow, 

 turning dark brown in preservatives. 



Female. — Carapace a little wider than 

 long and less than half the entire length ; 

 fourth segment less than half the width 

 of the genital segment, strongly nar- 



IW"!^ ' '1^ rowed in front of the fourth legs ; geni- 



1 ' tal segment flask-shaped, narrowed ante- 



riorly, emarginate posteriorly, with 

 broad lobes but no leg rudiments. 



Abdomen 2-segmented, the basal seg- 

 ment four times as long as the terminal ; 

 caudal rami minute and widely sepa- 

 rated. Furca large and broadly U-shaped ; fourth legs 4-segmented, 

 with four spines and a seta. Total length, 7-8.4 mm. 



Male. — Carapace elliptical, longer than wide, and much more than 

 half the entire length ; fourth segment spindle shaped ; genital seg- 

 ment orbicular, as wide as long, with two pairs of leg rudiments at 

 the posterior corners. Abdomen half the length of the genital seg- 

 ment, made up of a single segment, considerably narrowed basally. 

 Fourth legs scarcely reaching the center of the genital segment, their 

 basal segment unarmed. Total length, 4rA.b mm. 



FiGUEE 257. — Lepeophtheirus 

 thompsoni: a. Female, dorsal ; b, 

 female, fourth leg 



