110 MB. THOMAS SCOTT ON THE 



approximate proportional lengths of all the joints are shown by 

 the formula : — 



Proportional lengths of the joints . . . 17 . 21 . 15 . 13 . 6 . 10 . 5 . 4 . 6 ^ 

 Numbers of the joints 1 2 3 45678 9' 



The posterior foot-jaws (fig. 5) are stout ; the hand somewhat 

 resembles that of Thalestris rufoviolascens, but the inner margin 

 is more oblique and the marginal spinules are larger ; the other 

 mouth-organs are somewhat similar to those of Thalestris mysis. 

 The first pair of thoracic feet are moderately stout, and both 

 branches are armed with strong terminal claws (fig. 6). In the 

 fourth pair the inner branches only reach to about the end of 

 the second joint of the outer branches ; both branches bear long 

 plumose setse (fig. 7). The fifth pair are large and foliaceous : 

 the length of the basal joint is scarcely equal to twice the 

 breadth ; this joint bears five setse on the broadly rounded apex, 

 two of the intermediate (fig. 8) are considerably longer than the 

 others : the secondary joint is oval in outline, its greatest breadth 

 is equal to about half the length, and both the inner and outer 

 margins are fringed with minute cilia ; this joint is furnished 

 with six setse, three on the lower half of the outer margin and 

 three at the apex, — the two outer apical setse are close together 

 and more slender than the others, which are moderately wide 

 apart as shown in the figure. The caudal furca (fig. 9) are 

 elongate, being fully twice the length of the last abdominal 

 segment, and the two principal setse are as long as the whole 

 length of the abdomen and furca combined. ISTo males of this^ 

 species were observed. 



Hah. Half mile off Cape G-ertrude in 8 fathoms, June 6th, 

 1897 ; about fifty yards ofi" West Point, Cape Flora, in 2-3 

 fathoms, June 20th; and off "West Glacier, in 1-3 fathoms, 

 July 6th, 1897. 



The species was of rare occurrence in these gatherings. 



Hemarks. The large size of Thalestris JacTcsoni, the peculiar 

 form of the posterior foot-jaws, and the form and armature of the 

 large foliaceous fifth pair of thoracic feet, combine to distinguish 

 this from any other Thalestris known to me. This fine species 

 is named in compliment to Mr. Jackson, of the Jack son-Harm s- 

 worth Arctic Expedition. 



