114 BRITISH PARASITIC COPEPODA. 



observed projecting beyond the edges of the gill- 

 filaments. Frequently observed on halibut brought 

 to the Fish-Market at Aberdeen. 



The males are apparently very rare. Though many speci- 

 mens of halibut have been examined, only one male specimen 

 of this species has been met with. 



2. Hatschekia mulli (P. J. van Beneden). 

 (Plate XXXII, figs. 1-11.) 



1851. Clavella mulli P. J. van Beneden. (11) p. 99, pi. iii, figs. 3 & 4. 

 1896. Clavella mulli Bassett-Smith. (7) p. 159. 

 1906. Clavella mulli Norman & T. Scott. (88) p. 215. 



Female. Body narrow, elongated, and sub-cylin- 

 drical ; head small, subglobose, but the width rather 

 greater than the length ; front somewhat lobate and 

 without any horn-like processes. Neck very short, 

 the thorax, which is indistinctly segmented, merging 

 almost imperceptibly into the genital segment ; on the 

 dorsal aspect of the thorax, and on each side of the 

 median line, a small rounded protuberance, seen best 

 in lateral view (PL XXXII, fig. 2). Genital segment 

 elongated and narrow, slightly expanded in the middle 

 and tapering gradually towards both ends, greatest 

 width equal to about one-fourth of the entire length 

 of the animal; posterior end trilobed, lateral lobes 

 small and distinct, and produced slightly outwards, 

 the middle one broad and not very prominent. 



The cephalothoracic appendages comprise the 

 antennules, which are moderately small and composed 

 of three spinulose joints, the last one with also a few 

 apical spines ; the antenna?, composed each of a single 

 large and moderately long basal part, and furnished 

 with a stout terminal hook-like claw ; there is also at 

 the base of each antenna a small secondary appen- 

 dage probably a sense-organ (PL XXXIII, fig. 5). 

 Mandibles small with the extremity slightly curved 

 and hook-like. Maxillee small, with both the internal 

 and external rami considerably attenuated. Second 

 maxillipeds moderately slender and somewhat similar 



