414 



BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



TREBIUS TENUIFURCATUS Rathbun 



Figure 261 



TreUus tenuifurcatus Rathbun, Proc. U. S. Nat. Mus., vol. 10, p. 559, pi. 29, 

 1887.— Wilson, Proc. U. S. Nat. Mus., vol. 31, p. 679, pi. 15, 1907 ; vol. 35^ 

 p. 447, pi. 72, 1908. 



Occurrence.— Found on the outside surface of a sting ray captured 

 in the fish nets at Menemsha Bight, Marthas Vineyard. 



Distribution. — Y^ood^ Hole (Rathbun): San Diego, Calif 

 (Wilson). 



Color. — Body a uniform yellowish white with a very scattered 

 tracery of minute spots and lines of a bright reddish brown. These 



are widely scattered on the carapace 

 and free segments but are closer to- 

 gether on the genital segment and 

 along the lateral margins of the abdo- 

 men. Eye bright ruby-red. 



Female. — Carapace one-third wider 



than long, lateral lobes wide and 



blunt; eyes large and prominent; third 



segment much narrowed posteriorly; 



fourth segment the same length and 



width, rhomboidal; genital segment 



flask-shaped, narrowed anteriorly, with 



four large spines at each posterior 



corner on the dorsal surface and one 



pair of leg rudiments on the ventral 



surface. Abdomen five times as long 



as wide, 2-segmented, segments about equal; maxillae bipartite; 



f urea with elongate rami ; endopod of fourth legs 3-segmented. 



Total length, 4^.65 mm. 



Male. — Carapace as long as wide; third segment much shorter 

 than the fourth but wider; fourth segment wider than genital seg- 

 ment and two-thirds as long ; genital segment longer than wide, with 

 two pairs of leg rudiments. Abdomen 2-segmented, terminal seg- 

 ment twice the length of the basal; branches of furca curved like 

 parentheses. Total length, 1.75-2.25 mm. 



Remarks. — Rathbun's original description of this species was from 

 a single female, which had evidently shrunken in the preservative. 

 Since then fresh specimens of both sexes have been obtained, and 

 the description has been completed as above. The species can be 

 recognized by the large dorsal spines at the posterior corners of the 

 genital segment in the female. 



FiGDEB 261. — Trebius tenuifurcatus: 

 a. Female, dorsal ; 6, female, fourth 

 leg 



