Crustacea. 5285 



It is a perfectly translucent species, the large black eyes being the 

 chief points by which it can be detected. It is very graceful in its 

 movements, and, unless when much disturbed, it hovers very quietly 

 and elegantly about and among the bunches of pendant sea-weed ; 

 but when disturbed it instantly seeks shelter either at the bottom or 

 in some crevice. It is a small species, and, like all the others, has a 

 very slender form. It varies from one-quarter to nearly an inch in 

 length, and is of nearly equal diameter throughout. The carapace is 

 very nearly two-thirds as long as the abdomen, and its sides are nearly 

 parallel to each other and rather compressed. The rostrum is ob- 

 tusely triangular, is as long as the peduncles of the eyes, and is stout 

 and well marked. The eyes are rather large, and lie close on each 

 side of the rostrum ; they reach as far anteriorly as about the middle 

 of the lower joint of the base of the internal antennae. The internal 

 antennae are beneath the eyes, and between them and the rostrum ; 

 the lower of the basal joints is about twice as long as broad; the 

 second is small, compressed and more or less globular ; the third is 

 slightly longer than it is wide, and the distal extremity is enlarged to 

 allow of the articulation of the two terminal filaments, the external of 

 which is the largest, and is ornamented on the median margin near 

 the base with numerous flexible hairs, which bend in a semi-recum- 

 bent manner. The hairs on all the other parts are short and thinly 

 scattered. On the internal angle of the base of the antennae are one 

 or two bunches of long setae. The external antennae are the largest 

 and longest, and are situated below and a little externally to the inter- 

 nal ones. The terminal basal joint is about twice as long as the eye- 

 stalk, and the terminal filament is about as long as the body of the 

 creature. The antennal scale is large, extending beyond the basal 

 joints; its internal edge is straight, and terminates anteriorly in a 

 stout spine ; the anterior margin is convex, and clothed with long hair 

 closely arranged, which also extends along the inner margin. The 

 abdomen is about one-third longer than the carapace, and gradually 

 decreases in size to the caudal extremity. The middle plate of the 

 tail is obtusely lanceolate; the apex is truncated, the angles rounded, 

 and on each of these rounded portions is a large diverging spine, with 

 a smaller one between. The external caudal plate is longer than the 

 others, and at the external posterior margin there is a contraction, 

 which is covered with short hair, while the remaining portions are 

 clothed with long and closely arranged hair. The second plate is as 

 long as the central one, and is also clothed or margined with long 



