of the Fishery Board for Scotland. 75 



may only be a somewhat abnormal variety of the more common P. bicolor. 

 This form has scarcely any trace of the brown colouration so conspicuous 

 in P. bicolor ; it is also rather broader in proportion to the length. The 

 second dorsal plate is as wide as the posterior part of the cephalic shield, 

 and the posterior margins of each of the two lobes is obliquely truncated 

 instead of being rounded as in the normal form. The lobes of the next 

 plate, which have their posterior margins somewhat evenly rounded, are 

 separated by a semicircular hollow and are not spread so widely apart as 

 in the normal P. bicolor. The anal lamina are also more prominent than 

 in the normal form. Till further specimens of this pale-coloured form 

 are obtained, I prefer to regard it as only an accidental variety of P. bicolor. 



Genus Hatschekia, Poche (1902). 

 (syn. Clavella, Oken, nee. Cuvier). 

 Hatschekia cornigera, sp. n. PL III., figs. 1-7. 



I found this Copepod moderately frequent on the gills of several 

 specimens of Sea Bream, Pagellus centrodontus, De la Roche, sent to the 

 Laboratory from the Fish Market at Aberdeen. The species, however, does 

 not appear to be generally common, for a considerable proportion of the 

 fishes examined had their gills apparently free from the parasites. 



Hatschekia cornigera is a small species, and measures only about 2 '4 

 millimeters in length exclusive of the ovisacs, which are moderately 

 elongated. It is, like some other species of the same genus, of a narrow 

 elongated form (fig. 1), but may be distinguished from them by the 

 cephalon beiug produced backwards in the form of a short blunt-pointed, 

 spur-like process on the median dorsal aspect, as in the drawing (fig. 2), 

 which shows a profile view of the head and part of the thorax. 



The antennules are short, stout, and five-jointed, and sparingly setiferous, 

 the third and last joints being shorter than the others (fig. 3). 



The antennae are small, but being armed with stout terminal hooked 

 spines they form effective grasping organs (fig. 4). 



The mandibles, maxilla?, and maxillipeds do not appear to differ greatly 

 from the corresponding appendages of other members of the genus. 

 Figure 5 represents one of the second pair of maxillipeds ; they are each 

 three-jointed, moderately elongated, and armed with a stout terminal 

 claw which is bifurcated at the extremity ; the second joint bears also a 

 small curved spine near its proximal end ; there is also a small seta at the 

 base of the terminal claw. 



The thoracic limbs comprise apparently only two pairs, as in other 

 members of the genus. Both pairs are somewhat alike in structure, but 

 the first are considerably smaller than the second pair. One of the first 

 pair is represented by figure 6 ; it consists of a moderately stcut, two jointed 

 basal part and two, two-jointed branches. The inner branch is rather 

 shorter than the outer, and the first joint is shorter than the end one ; in 

 the outer branch the joints are nearly of equal length. Both branches are 

 furnished with several stout spines. In the second pair, one of which is 

 represented by figure 7, the inner branches are stouter and rather longer 

 than the outer, and the end joint is about twice the length of the first. In 

 the outer branch the end joint is the smallest. Both branches are 

 furnished with a few terminal spines, one cf which is considerably stouter 

 and rather more elongate than the others. 



The colour of the parasites resembles that of the gills of the fish. 



