IDYA. 173 



All the joints are somewhat sparingly setose, and the 

 fourth bears a long curved (olfactory?) appendage 

 (fig. 2, a) ; in the male (fig. 3) the median joints are 

 swollen and coalescent, and the terminal joints are 

 constricted at the points of articulation. The posterior 

 antennas are 3- jointed (fig. 4), and bear several 

 terminal setas, five of which are geniculated ; the 

 inner branch is long and 4-jointed. First and second 

 foot-jaws (figs. 7, 8) slender, with long curved claws. 

 The inner branch of the first pair of feet consists of 

 two long joints, the first of which is much dilated 

 above ; each joint bears a very long plumose marginal 

 seta (fig. 9, a, a), and the last is armed at the apex 

 with two slender claws ; outer branch 3- jointed, short, 

 and broad ; last joint very small and truncate, armed 

 with seven moderately long and stout setaa, the five 

 shorter of which bear on their concave margins a few 

 secund spine- like apical cilia; the first and second 

 joints also bear each a single stout plumose seta. 

 Fifth pair of feet (fig. 11) 2-jointed, first joint short, 

 setiferous at the angles, second elongated, marginally 

 ciliated, and at the apex bearing five long setaa, smaller 

 in the male. Fourth and fifth abdominal segments 

 very short ; caudal segments short, about as long as 

 broad. Inner tail-seta nearly as long as the body of 

 the animal, outer about half as long, both finely 

 aculeate in their entire length. Animal usually colour- 

 less or pale milky white, often yellowish, and some- 

 times distinctly banded with pale lilac or purple. 

 Length -^-th of an inch (1 mm.). 



This species is almost ubiquitous in the British seas. 



