700 CRUSTACEA. 



ninth of an inch. The body is broadest anteriorly. There are only 

 six thoracic segments, the normal first being probably concealed by 

 the following. The abdomen has three segments, besides an appear- 

 ance of another, anterior to these, situated mostly beneath the last 

 thoracic segment. Of the three segments alluded to, the first two are 

 very short; the last is oblong, narrows behind, and is regularly rounded 

 at its extremity, with a few short ciliations. Only six pairs of legs 

 were distinguished, three posterior and three anterior. The eyes were 

 situated on the angles of the head, and were a little prominent. 



The outer antennae have basal joints, and a terminal portion con- 

 sisting of three joints ; the first four basal joints are short ; the fifth 

 oblong. The inner antennas are quite short; the third joint is longer 

 than the fourth. 



Figures 1 h and 1 i, are from a specimen six lines long, collected 

 near New Zealand, and probably identical with I. argentea. The 

 abdomen is very similar. The outer antennae have the flagellum 

 about as long as the base, and eight-jointed ; surface minutely scabrous, 

 under a high magnifier. 



Idot^ea margaritacea. 



Plate 46, fig. 2 a, animal, enlarged; 5, caudal extremity; c, outer 

 antennae ; d, extremity of flagellum of another specimen. 



Length, five lines. Colour, bluish, with the back pearly white. 

 Differs from the preceding somewhat in its antennae and front of 

 head ; and the body is not quite as much narrowed behind. The 

 three teeth of the front are very low; one occupies either angle, and 

 the third, which is less distinct, the middle of the front; the outer 

 are subacute ; the spaces between are low concave. The inner an- 

 tennae extend to apex of antepenult joint of base of outer antennae, 

 and there are a few short setae at apex on outer side. The outer 

 antennae have the third joint two-thirds the following, and the fifth 

 four-thirds the fourth, but this may not be constant; the flagellum 

 has but four or five joints, the number being five through a subdivi- 

 sion of the first of the four when four-jointed. The surface of the 



