DISCOVERY REPORTS 



Ant.2 

 Mand- 



Mandible segment i with a strong spine, but without molar process ; exopod with five 

 setae; endopod an undivided plate, with six setae or spines. 



Stage III, R. cornutus. Length 0-65-0-70, average o-66 mm. 



Body more elongated, the length about 3 J times greatest width. Furcal region 

 (Fig. 2 C) cleft, each branch bearing a short spine on ventral surface, a terminal spine, 

 and an inner terminal soft seta. The right spine is longer than the left, but only about 

 one-tenth length of body. 



Antennule with six terminal setae, but no aesthete. (Fig. 2B.) 



Antenna, exopod with eight setae. 

 There is no trace of the maxillule. 



/\ Stage IV. Length: R. nasutus, 0-82- 

 0-89, average 0-85 mm. ; R. cornutus, 

 i-o mm. 



Body now very slender, five times as 

 long as wide. Furcal region with two 

 additional pairs of lateral spines. In 

 R. nasutus the furcal spines have scarcely 

 increased in length, so that the right 

 spine is now shorter in proportion to 

 the body, and not greatly longer than 

 the left one (62 : 49). In R. cornutus it 

 is nearly one-third of the length of the 

 body (60 : 195) and about 2 1 times as 

 long as the left spine (57 : 22). 



Mandible with strong molar process 

 on coxa. 



Antennule with eight setae and aes- 

 thete, arranged thus: 5-A-3. 1 In some 

 specimens of R. cornutus the maxillule 



Fig. 6. Rhincalanus cornutus. Nauplius, stages V and VI. « represented by a slight fold with a 

 A, upper lip, stage VI, showing arrangement of hairs on small projecting spinule, but I have 

 body wall; B, mandible, stage V. seen no trace of it in R. nasutus. 



Stage V. Length: R. nasutus, 1 mm.; R. cornutus, 1-2 mm. 



Antennule with 7-A-4 terminal setae. 



Maxillule distinct, as a small fold bearing a small seta. 



Maxilla traceable as a faint fold with a minute spine. 



Body distinctly divided into an anterior region including the somite of the maxilla, 



1 The arrangement of the setae on segment 3 may be conveniently expressed in this way: the first 

 number being the setae behind the aesthete (A), and the second those in front of it. 



