LARVAE OF SERGESTES 



3S 



than in 5. robustus, but those of somite 5 nearly as long as somite 6. Telson about 

 i| times as long as wide, the lateral spines well in front of fork. Arms of fork slender, 

 parallel, with two outer and two inner spines, the two outer spines widely separated. 



Eye about one-sixth length of body; length of eye i^ times width of eyeball; papilla 

 present. Exopod about nine times as long as wide ; setose part of margin slightly longer 

 than bare part. 



Stage 2. Length 3-95 mm. Rostrum 1-5 mm. 



As stage i, but scale with distal spine. Pleopods rather small, without endopods. 

 Uropod a little broader, and setose part equal to bare part. Lateral spine of telson 

 placed farther forward. 



1\ 



a 



Fig. 27. S. robustus A. Mastigopus telson. a, 7-2 mm. ; b, 5-7 mm. ; c, 8 mm. ; d, 9 mm. ; 

 e, the same, branch enlarged to show inner spines;/, 1 1-6 mm. ; ^, 15 mm. 



We have no Mastigopus corresponding to the Acanthosoma of form B, but several 

 which apparently belong to form A. Measurements of these have been made to compare 

 with specimens from Bermuda which are presumed to be typical S. robustus but these 

 do not reveal any differences which can be regarded as of specific value. The telson, 

 however (Fig. 27), has the same differences as are seen in the Acanthosoma. It appears 

 that form A is a species definitely recognizable as distinct in early larval stages but 

 becoming indistinguishable from S. robustus in advanced Mastigopus stages. 



S. robustus Form C 



Material. One specimen of the Acanthosoma was taken in 1935 at Bermuda. The 

 Elaphocaris stages described here were taken at Bermuda in 1939 and their reference 

 to this robustus form is quite speculative. Stage i was connected with stage 2 by moult. 



An Elaphocaris of the same form has already been described (Gurney, 1924, figs. 26, 

 28) from New Zealand. 



5-2 



