GROUP a 



241 



showing natural relationships they are less reliable than the characters of the male 

 copulatory organs. 



Just as differences in antennular characters may mask, or at least not show specific 

 affinities, so similarities in them may either correspond with true affinities or give the 

 appearance of affinity where there is none ; though it is no doubt more probable that 



a bed 



Fig. 27. Male copulatory organs of the species of the gibba group, a, E. gibba ; b, E. pseudogibba ; 

 c, E. Iiemigibba; d, E. pamgibba; after Hansen. 



they would do the former than the latter. I believe both to be illustrated in Hansen's 

 gibba group, the four species E. gibba, E. pseudogibba, E. hemigibba and E. paragibba 

 (Hansen, 1910). He wrote (1912, p. 245) : "£. gibba is closely allied and very similar to 

 E. pseudogibba, E. hemigibba and E. paragibba. These four species are in reality so similar 

 in general aspect, in shape of rostrum, size of eyes, lobe of first antennular joint, etc., 

 that a close examination is necessary in order to separate them. As pointed out in the 

 Siboga Report the male copulatory organs of the first pleopod afford excellent specific 

 characters, and it may be added that these organs in E. gibba differ strongly from those 

 in the three species mentioned.. . ."1 They differ so strongly that there can be little 

 doubt that E. gibba is not related to them (Fig. 27). The copulatory organs of E. pseudo- 

 gibba, E. hemigibba and E. paragibba are so unlike those of any others and, despite strong 



' And, as Hansen recognized, from those of any other species of Eiiphausia. 



