212 "TERRA NOVA" EXPEDITION. 



A. glacialis differs from A. antarctica : — 



(1) lu the size of the eyes. PI. IV, figs. 1, 2, 3. 



In the type specimen, measuring 37 mm. in lengtli, the head measures 

 7 mm. in a straight line across its widest part. The eyes measure 2 • 5 mm. 

 along their longer axes, and the distance -between the eyes is less than the 

 length of the longest axis of each eye. The eyes are of elongate pyriform 

 shape, the longer axis running transversely across the head towards the 

 centre with the narrower end of the eye nearer the centre. The pigment 

 is somewhat paler than in A. antarctica. 



In a specimen of A. antarctica, 25 mm. in length, the head measures 

 6 mm. in greatest width, the longest axis of the eye measures 1 '25 mm., and 

 the distance between the eyes is 3 • 5 mm., or more than double the length of 

 the longest axis of the eye. The eye is of a much shorter pyriform shape 

 than in A. glacialis, as if the elongate narrower end of the eye in the latter 

 had become obsolete, while the pigment is much blacker. 



(2) In the armature of the anterior thoracic limbs. 



In A. antarctica, according to Hodgson, and the specimens in the present 

 collection bear out his description, the propodus of the second to fourth 

 thoracic limbs is armed with three blunt spines on the inner margin, one at 

 either end and one intermediate, while the carpus has three such blunt spines. 



In ^. glacialis both propodus and carpus of the second to fourth 

 thoracic limbs have only one spine each, at the distal end of the inner margin 

 (pi. IV, fig. 8). 



(3) In size. 



The largest A. antarctica recorded hitherto measures 28 mm. A. glacialis 

 reaches 38 mm. in length. 



For the rest, the body in A. glacialis is rather more than twice as long- 

 as broad, perfectly smooth and without hairs. The telson is rather less in 

 length than one-quarter of the entire animal, and one and a quarter times as 

 broad, at its widest part, as long. There is a well-developed keel in the 

 mid-dorsal line, and the margins are produced into a short acute apex, 

 minutely crenulated distally, with short setae between the crenulations. The 

 uropods are slightly longer than the telson, both with rather acute apices, 

 their margins crenulate and armed with short setae. 



The peduncle of the antennule (pi. IV, fig. 5) is as long as the head, and 

 has the third joint considerably longer than the first two combined. The 

 flagellum has about twenty joints. 



The antenna (pi. IV, fig. 6) reaches the posterior end of the third free 

 thoracic somite. The fourth joint of the peduncle is level with the end of the 



