64 BRITISH PARASITIC COPEPODA. 



Dr. Bassett-Smith obtained four specimens of this curious 

 parasite on the inside of the operculum of a maigre captured 

 at Plymouth. Though this is the only British record of 

 Scisenophilus we know of, Professor P. J. van Beneden states 

 that the species is very common on the maigre, and he has 

 seen such a great number of specimens crowded together that 

 they resembled tufts of moss (" formant des touffes semblables 

 a une mousse"). This fish is not common in the British 

 seas, and, according to Aflalo, is taken only casually in the 

 mackerel nets, and this probably is the reason why such a 

 common parasite as this appears to be has not been more 

 frequently recorded. 



Scisenophilus tenuis, so named from its narrow and elon- 

 gated form, has at first sight a close resemblance to a Hat- 

 sehekia (Clavella), but the form and structure of the carapace 

 reveal at once its near relationship with Caligus. 



Genus 7. LEPEOPHTHEIRUS Nordmanu, 1832. 



Free thoracic segment without dorsal plates. Genital 

 segment simple. Abdomen one- or two-segmented. 



Mandibles serrated only on the inner edge. Second 

 maxillae small, furcate, the branches acuminate, not 

 simple and spine-like as in Caligus. Fourth pair of 

 thoracic legs and other thoracic appendages as in 

 Caligus. 



Both the females and the males have a general 

 resemblance to those of Caligus, but the frontal plates 

 are without lunulse. 



1. Lepeophtheirus pectoralis (0. F. Miiller). 



(Plate X, figs. 3-4 ; Plate XII, figs. 2-3; Plates XIII, 

 XIV, XV; and Plate XVI, figs. 1-3.) 



1777. Lernsea pectoralis O. F. Miiller. (85) Zool. Danica, p. 41, pi. 

 xxxiii, fig. 7. 



1838. Caligus pectoralis Kroyer. (70) (ii), p. 8, pi. vi, fig. 4. 



1832. Lepeophtheirus pectoralis Nordmann. (89) p. 30. 



1847. Caligus pectoralis Thompson (129), p. 247. 



1850. Lepeophtheirus pectoralis Baird. (4) p. 275, pi. xxxii, fig. 10. 



1900. Lepeophtheirus pectoralis T. Scott. (112) p. 150, pi. v, figs. 

 26-31. 



Female. Carapace suborbicular, length and widtli 

 nearly the same, and scarcely equal to half the entire 



