38 DISCOVERY REPORTS 



Eye about one-seventh length of body; eyeball nearly round, its width nearly half 

 length of eye. Antennal scale rather broad, with long apical spine; flagellum 2-i mm. 

 long. Mandible with rudimentary palp. Pleopods long, with small rudiments of endo- 

 pods on 2-5. Exopod of uropod widening distally, its length about five times the width ; 

 bare margin 17 times as long as setose. The form of the exopod is not quite correctly 

 shown in the figure — it should be broader at end. 



Colour. Red round dorsal organ and in sides of thorax ; down middle of abdomen ; 

 in eye, antennal scale and both branches of uropod. 



Sergestes corniculum Kroyer 



Hansen, 1922, pp. 134, 136, Mastigopus and Acanthosoma. 



Gurney, igz^c, figs. 21, 22, 23 (?). 



Cecchini, 19286, p. 35, Acanthosoma and Mastigopus. 



We are indebted to Mr M. D. Burkenroad for valuable information regarding this 

 species. He informs us that S. corniculum, as described by Hansen, includes two species, 

 and that there are at least three species of this group in the North Atlantic. In material 

 from Bermuda which we have submitted to him he has recognized two distinct forms, 

 but he is not at present able to give a final opinion or names for the species which he 

 has distinguished. We had already found that there are two distinct larval forms at 

 Bermuda. One of these, which we designate as form B, is identical with Hansen's 

 Acanthosoma, and has been found also in several of the Discovery samples. The second, 

 form A, was common in the summer of 1939, but was very rare in the spring of 1935, 

 whereas form B was more common in 1935 and was taken rarely in early summer of 

 1938. The Elaphocaris was not moulted to Acanthosoma, but the colouring, general 

 appearance and occurrence with the Acanthosoma, together with elimination of other 

 species, make the identification with S. corniculum s. lat. practically certain. Two forms 

 of Elaphocaris were taken in 1935, differing only in the number of spines on the 

 carapace. Of these the form described as belonging to form A was the only one taken, 

 with one exception in stage 2, in 1938-9. Since form A Acanthosoma was by far the 

 more common in that period, it is assumed that the rarer form of 1935 belongs to 

 form B. 



Of form A the first Elaphocaris was moulted to stage 2, and Acanthosoma to Masti- 

 gopus. Mastigopus stage 2 was also obtained from stage i. Mastigopus i was also 

 obtained from the Acanthosoma in 1935. 



A third form of Acanthosoma, which evidently belongs to the same superspecific 

 group, is described below as S. corniculum C. This was not found at Bermuda, but at 

 three of the Discovery Stations, two off the African coast and one near the coast of 

 South America, all three near the equator. 



