552 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.55. 



tail and accurately figured by Cornalia in 1865. But the name Lo- 

 phoura had been preoccupied by Fleming in 1822 for a genus of birds, 

 and hence Poche in 1903 proposed the new name Eebelula, which 

 has been adopted. 



P. J. van Beneden discovered a parasite Avhich he described and 

 figured in 1851 as Lcrnaeonema musteli; this was renamed Trypaphy- 

 lum musteli by Richiardi (1878), who added nothing to the descrip- 

 tion. But later T. and A. Scott (1913) supplemented the description 

 of the female and added one of the male, with excellent figures of 

 both sexes (p. 159, pi. 45, fig. 6; pi. 51, fig. 1; pi. 49, figs. 1-7). 



ECOLOGY. 



Sexual dimorphism. — The female sphyriid is a fixed parasite and 

 has completely lost not only the power of locomotion but also the 

 swimming legs and often most of the other appendages. Further- 

 more her body has been transformed in size and structure to a greater 

 extent than in any other family of copepods. Consequently we find 

 here very marked sexual dimorphism in locomotion, in prehension, 

 and in morphology, which will be taken up under these headings 

 respectively. 



Locomotion. — Although we know nothing of the development of 

 any genus in the family, we are safe in saying that the larvae alone 

 possess the power of free swimming, but we can only surmise for how 

 long a period it continues. During this period, whatever its length 

 may be, both sexes fasten upon their future host, after which their 

 subsequent development varies greatly. 



Female. — We are not obliged to suppose that the female eventually 

 fastens to the first spot upon the fish's body that she happens to come 

 in contact with. In all probability she can move about over the 

 external surface and thus exercise a choice as to her final location. 

 It may fairly be said that this is proved by the fact that so many 

 of the species are found fastened near the base of the dorsal fin. It 

 would hardly be possible for them all to hit that spot upon their first 

 trial. The necessary locomotion over the surface of the body of the 

 host is accomplished by means of the maxillae and maxillipeds as in 

 the male. But, having once reached a suitable and satisfactory loca- 

 tion, and having commenced to burrow, all locomotion on the part of 

 the female ceases and she becomes permanently fixed for life. 



Male. — Similarly the male moves about over the surface of the 

 host, and also over the body of the female, after he has once fastened 

 to her. This movement is accomplished by means of the second 

 maxillae and maxillipeds, in a manner similar to that of the Lernae- 

 opod male. In the genera Rehelula and Sphyrion the structure of 

 the antennae shows them to be absolutely unfit to take any part in 

 locomotion. And in Paeon, while the second antennae are furnished 



