46 



DISCOVERY REPORTS 



very small papilla. Antennal scale slender, with very long apical spine ; flagellum long 

 (broken). In stage i the scale has three stout apical setae and small spine and seta near 

 end on outer side ; flagellum unsegmented, twice length of scale. Pleopods long, with 

 rudimentary endopod on 2-5. Uropod very slender, the setose margin twice length of 

 bare part. 



Mastigopus I (Fig. 37 a, b). Length 3-85 mm. Rostrum o-6 mm. 



Diff"ers from S. cornicidum A in shape of eye, which is relatively shorter and with 

 smaller eyeball. The pleural point of somite 5 is shorter, and the setose part of the 

 uropod more than twice the bare part. Otherwise the two forms are indistinguishable. 



Fig. 37. S. corniciibmi C. a, Mastigopus i ; h, telson. 



Remarks. This Acanthosoma is very much like that of S. corniculum A, but differs 

 in shape of eye and the great length of the dorsal spines of the abdomen. In the form 

 of the eye it resembles the Acanthosoma attributed to S. seyninudus Hansen (Hansen, 

 1919, p. 20), but that form has much shorter dorsal spines, and is not found in the 

 Atlantic so far as is known. 



Group II 



Hansen's group II, with very large maxillipede 3, includes six Atlantic species. Of 

 these S. pectinatus and S. sargassi seem to be so closely related that their larvae may be 

 expected to be very similar. We know nothing certainly about the development of 

 S. sargassi, but we have most of the stages of S. pectinatus, and its larvae differ distinctly 

 in many respects from those of S. vigilax, for example. The larvae, in fact, support a 

 division into two subgroups. 



If all the Acanthosomas having a short, forked telson of the form known in S. vigilax 



