52 DISCOVERY REPORTS 



uropod with outer spine large ; setose margin one and a half times as long as the bare 

 part. 



Colour. Very red, mainly in abdominal somites 1-3 and 6. 



At a body length of 5-6 mm. the rostrum is reduced to a minute point, though the 

 supraorbital spines are of fair size. The endopods of the pleopods are setose. 



In specimens of 678 mm. and 8 mm. 

 there is no trace of the rostrum. The outer 

 marginal spine of the uropod is retained at 

 8 mm. 



Remarks. The Mastigopus of S. pecti- 

 natus and S. sargassi can be readily dis- 

 tinguished in life by colour, the latter being 

 deep crimson and pink all over, except for 

 the telson, uropods and appendages, which 

 are colourless. The flagellum seems to lack 

 the red bands which are seen in S. pectinatus. 



Structural differences are as follows: 



(i) Terminal spinous process of carpus 

 of maxillipede 3 in S. pectinatus. 



(2) Much greater length of the setose 

 part of the uropod in S. pectinatus, in which 

 it is never less than twice the bare part, and 

 may be three times as long; whereas it is 

 not much more than i\ times in S. sargassi. 

 The latter retains the marginal spine longer 

 than 5. pectinatus. 



(3) The shape of the eye is distinctive, 

 but difficult to describe. It may be said 



Fig. 44. S. sargassi. Mastigopus 2 ? 



that the long diameter of the eyeball is markedly greater in S. pectinatus, whereas the 

 eyestalk is distinctly shorter. 



(4) S. sargassi is somewhat larger at equivalent stages. 



The synonymy of this species seems to be rather obscure, and we have accepted 

 Hansen's position. lUig's figures of the Mastigopus of S. henseni and S. ntidus are not 

 sufficiently complete for certain identification, but it may be suggested that Figs. 84 

 and 104 are of S. pectinatus and Fig. 103 of S. sargassi. 



