BRACHIELLA THYNNI. 205 



spines. First maxillipeds short, stout, and strongly 

 uncinate. The second maxillipeds, which are equal 

 to about two-thirds of the length of the genital seg- 

 ment, slender and free except at the tip, where they 

 are joined to a reddish-brown coloured chitinous plug. 

 Length from the forehead to the end of the posterior 

 appendages of a full-grown specimen about 32 mm. ; 

 length of cephalothorax about 14 mm., of the genital 

 segment about 9 mm., and of the posterior appendages 

 9 mm. 



Male. Very small, being about a millimetre in 

 length ; having a closer resemblance to the male of 

 Lernaeopoda than to that of a true Brachiella. 



Habitat. Parasitic on the gills of the tunny (Om/- 

 nus thynnus), and other nearly related fishes. Four 

 specimens were obtained by Dr. Bassett-Smith on a 

 tunny captured at Plymouth. 



The female of this species is somewhat similar to B. rostrata 

 in general appearance, but the cephalothorax is distinctly 

 longer, and the posterior appendages are four in number and 

 much more elongated. 



2. Brachiella rostrata Kroyer. 



(Plate XLV, fig. 8 ; Plate LXII, fig. 3 ; Plate LXIII, 



figs. 2-8.) 



1837. Brachiella rostrala Kroyer. (70) Rekka 1, p. 207, pi. ii, fig. 1. 



1840. Brachiella rostrata M. Edwards. (43) vol. iii, p. 415. 



1863. Brachiella rostrata Kroyer. (71) p. 290, pi. xviii, figs. 8, a-i. 



1877. Brachiella rostrata C. Vogt. (142) p. 426. 



1900. Brachiella rostrata T. Scott. (112) p. 174, pi. viii, figs. 38, 39. 



Female. Cephalothorax elongated, flexuose or 

 vermiform, and separated from the genital segment 

 by a more or less clearly-defined constriction. Genital 

 segment narrow, subcylindrical, fully three times 

 longer than broad and equal to about one and one- 

 third times the length of the cephalothorax ; posterior 

 end subtruncated and furnished with two subapical 

 appendages. Abdomen obsolete or nearly so. The 

 egg-strings, which are tolerably elongated, arising 

 immediately outside of the subapical appendages. 



