ISOMETRINAE 179 



of Stations, arranged in lines running out from the American coast to the 100 fathom 

 line, and covers a greater area, particularly to the north, the last line being in the latitude 

 of 44° S, than either of the two previous surveys. From it there are specimens of 

 /. vivipara from two stations only, the last two in the list above, both of them very near 

 the Falkland Islands. It is strange that it should not have been taken at any of the 

 stations farther from the Falklands, to the west and north and along the Patagonian 

 coast, especially since the depths of many of them fall within the range of those at which 

 the species occurred around the Falkland Islands; and especially since the species is 

 known to occur much farther north, for some of Mortensen's specimens came from the 

 coasts of Uruguaya and northern Argentina. 



Some of Mortensen's specimens came, too, from far south, from the east side of 

 Graham Land in the Antarctic. But from the trawl and dredge hauls made by the 

 Discovery vessels along the coasts of the Falkland Dependencies — many at South 

 Georgia, few at the South Sandwich and South Orkney Islands, and many in the 

 Bransfield Strait and on the west side of Graham Land — there is only one specimen of 

 /. vivipara. It is from the Bransfield Strait and, although it differs in some ways from 

 those described by Mortensen and from the remainder of the present collection, it is 

 not regarded here as a separate variety or species (see below). 



Distribution. /. vivipara is known from off the coasts of Uruguaya and north 

 Argentina; from around the Falkland Islands and on the Burdwood Bank; and from 

 the Bransfield Strait and the east coast of Graham Land in the Antarctic. 



Descriptive remarks. The 54 specimens from near the Falkland Islands and from 

 the Burdwood Bank agree fairly closely with Mortensen's description. They are up to 

 70 mm. in arm length. The majority are of a white or pale straw colour in spirit ; some 

 have a reddish tinge in parts as, for example, on the proximal cirrals; one is a light 

 brown and two a very pale yellow. In all the first seven or eight cirrals are slightly 

 darker than those beyond, which are white ; the change may be sharp or gradual. 



The number of cirri and the number of segments of which they are made may be 

 greater than Mortensen gives. Cirri up to LX, 26-43. The first two segments are short, 

 the third is longer. The fourth or the fifth is as long as broad. The fifth to about the 

 tenth may be longer than broad, the first of them appreciably so. The distal segments 

 are wider than long and are produced into dorsal spines which may be low as Mortensen 

 (191,8, p. II, fig. 7) shows but are often stronger; they may be stronger than those 

 shown in Fig. 15 a. The opposing spine is erect, the terminal claw short but strong. 



The normal positions of the first two syzygies are, as Mortensen says, between the 



third and fourth and the ninth and tenth brachials but there are many irregularities. 



In one specimen a first syzygy is between the sixth and seventh brachials. In others 



where the first syzygy is normally placed the second may occur between any pair of 



brachials between the fifth and the eleventh. In one specimen there is a chain of 



syzygies on one arm uniting each of the pairs of brachials from the third and fourth to 



the eleventh and twelfth, beyond which the sixteenth and seventeenth are the next 



syzygial pair. 



8-2 



