AMPHIPODA FROM BAY OF BISCAY. 217 



the sensory spines of the flageUum also show a marked difference, 

 being short and thick, and curved like hooks, while in pusilla they 

 are long and slender, and hardly curved at all. The fascicles of 

 plumose setae cannot be used as a distinguishing character, seeing 

 that it is only in certain stages of development that they occur in falcata, 



Gnatlio'pod 2. All the specimens taken by the Huxley are fully 

 adult, the two males showing the characteristic development of the 

 thumb. There are two forms of the hand in fakata, correlated with 

 the two forms of antenna. In the first form the hand is broad 

 and swollen, thumb broad and truncate at the apex. In the second 

 form the hand long and slender, with fascicles of plumose setae along 

 the palmar margin, and the thumb is long and narrow, tapering to a 

 subacute point. But in all the stages of development in falcata 

 the apical margin of the thumb is entire, with not the slightest 

 tendency to the bifid apex of the adult ;pusilla. The young male of 

 pusilla resembles the young male of the second form of falcata in the 

 development of the thumb, cf. figures given by Sars (30), pi. 212, 

 p. 2, (?^, and pi. 213, 1, p. 2, 6 -. 



Norman (27), p. 93, considers the Podocerus variegatus of Bate and 

 Westwood (not Leach) to be the female of pusilla, but an examination 

 of Bate's specimens in the British Museum has shown it to be the 

 female of the first form of falcata ; it has the broad, heavily-built, 

 inferior antenna, the short stout joints in the flagellum, and the second 

 sideplate and hand characteristic of this species. 



The finger in falcata develops with age an angular projection on the 

 inner margin, very noticeable in the full-grown male. The finger in 

 2)usilla shows no sign of it. 



The Feraeopocls afford another character for distinguishing the 

 species. In pusilla they are much longer in proportion to the 

 animal's size, and more slender, the 6th and 7th joints more elon- 

 gate; 7th joint lightly curved, not falciform as in falcata; 6th joint 

 lacking the stout sensory spines carried by the latter species. 



Distrihution. J. pusilla appears to be a deep-water form, there 

 being no authentic record of its occurrence in a less depth than 

 20 fathoms. J. falcata, on the other hand, is a littoral or sub-littoral 

 form, building its nests in the algae and hydroids on buoys, dock-piles 

 and rocks near the shore. 



J. pusilla has been recorded by : — 



Sars (29), p. 112, as Podocerus minutus, and (30), p. 597, as Podocerus 

 pusillus, from the south and west coasts of Norway, and as far north as 

 Hammerfest, " clinging to hydroidae growing in depths varying from 

 20-100 fathoms." 



NEW SEIUES. — VOL. IX. NO. 2. OCTOBER, 1911. P 



