258 



relatively shorter 2nd segment and a long distal part; the length of the 2nd 

 segment hardly exceeds its width and is approximately equal in length to 

 the 3rd-5th segments together, the posterior lobe extending far beyond 

 the base of the 4th segment; the anterior margin of the 2nd segment has 

 a slight transverse groove and a distal spinule; the 4th segment is broad- 

 ened distally; the length of the 5th segment is 2.5-3 times its width and 

 equal to the 6th; the 7th segment is narrow, finger-shaped, with complex 

 squamose pattern on the surface, and 2/3 the length of the 6th segment. 



The pleon and urosome are equal to the pereon in length. Uro- 

 somite I is narrower than the next (geminate) urosomite whose lateral 

 angles do not project backward. The basipodites of the uropods are longer 

 than the rami. The outer margin of the basipodite of uropods I is distally 

 denticulate; the rami are equal in length, 2/3 the length of the basipodite, 

 with coarsely denticulate margins. The basipodite of uropods II is nar- 

 rower, 2/3 the length of the basipodite of uropods I, with smooth mar- 

 gins; the endopodite is slightly broader and longer than the exopodite 

 and both have denticulate margins. The structure of uropods III differs 

 in females and males; the smooth basipodite is 1.5 times longer than 

 wide in females and two or slightly more times in males; the rami in 

 both sexes are finely denticulate except in the smooth proximal part of 

 the outer margin of the exopodite; in females the exopodite is narrower 

 than the endopodite but equal in length, which is slightly more than half 

 the length of the basipodite; in males the endopodite is broadened and 

 highly elongated, its length about 3/4 the length of the basipodite and 

 1/3 times more than the exopodite; the apex of the endopodite is round, 

 with a small seta in a notch. The telson is roundish-triangular, its length 

 equal to its width at the base. 



Distribution: Widely distributed in the tropical and temperate zones 

 of the three oceans, spreading in the North Atlantic up to 60° N, in 

 the Pacific Ocean up to 50° N and in the Southern Ocean up to the 

 Antarctic Convergence. Sometimes it is found in considerable numbers, 

 particularly in dense salp swarms. 



214 6. Vibilia robusta Bovallius, 1887 (Fig. 106) 



Bovallius, 1887a: 7; Behning, 1912: 213; 1927: 116; Stephensen, 

 1918: 31.—hirsuta Behning and Woltereck, 1912: 9. 



The largest species of Vibilia, with a body length up to 20 mm. 



Sexual dimorphism is manifest so weakly that only the presence 

 of oostegites or their rudiments serve as a reliable indication of the 

 sex. The body integument is very thick. The head is small, its height 

 somewhat more than its length, and the latter less than the length of 

 the first two somites of the pereon; the frons, particularly in large indi- 

 viduals, projects prominently over the base of antennae I. The eyes are 

 very large, occupying half or more of the lateral surface of the head, 



