CAL1GUS CENTRODONTI. 51 



proximal joint of the ramus short and scarcely half the 

 length of the other, and bearing a tolerably long straight 

 spine on its outer distal angle ; the end joint narrow 

 and provided with three terminal spines, the outer- 

 most similar to that on the preceding joint, the middle 

 one slender and nearly as long as the joint, and ter- 

 minating in a curved claw-like extremity, the inner- 

 most spine, a small one, appearing to be merely a 

 prolongation of the inner distal angle of the joint. 

 Fifth pair nearly obsolete. Egg-strings tolerably stout 

 but not very elongated. Length about 4 mm. 



Male. The male is somewhat similar to the female 

 but larger. A specimen examined by us, which was 

 found to be a male not a female as stated in the 

 Fishery Board's Report measured five millimetres in 

 total length. The carapace was suborbicular and 

 distinctly larger in proportion to the total length, 

 while the genital segment was much smaller than in the 

 female, and the posterior margin of this segment was 

 also more deeply concave, so much so that the postero- 

 lateral angles reached beyond, and enclosed the very 

 short abdomen. The caudal rami were also very short. 



Antennules and frontal plates tolerably large. 

 Second maxillipeds large, with the end-joint con- 

 siderably expanded and provided with a strong, hinged, 

 terminal claw, so as to form powerful grasping organs 

 as shown in the drawing (PL XVIII, fig. 2). 



Habitat. Parasitic on the tail and fins of the sea- 

 bream, Pagellus cent-rod ontus, and of the ballan wrasse, 

 Labrus bergylta. Dublin, 1837, on Pagellus centro- 

 dontus (Baird). Plymouth, on Pagellus centrodontn* 

 (Bassett- Smith). Moray Firth, on Labrus bergi/Jtn 

 (T. Scott). 



There can be no doubt that the species described by 

 Kroyer in 1863 under the name of Caligus abbreviate is 

 identical with Baird's C. centrodonti. The peculiar form of 

 the genital segment, the very short abdomen and caudal 

 rami, together with the structure and armature of the fourth 

 pair of thoracic legs, establish the identity of the two forms. 



