60 BRITISH PARASITIC COPEPODA. 



10. Caligus diaphanus Nordmann. 



(Plate XVII, fig. 1 ; Plate XVIII, figs. 6, 7 ; Plate 

 XL VIII, fig. 7.) 



1832. Caligus diaphanus Nordrnann. (89) pt. 2, p. 26 (non C. dia- 

 phanus, Baird). 



1863. Caligus diaphanus Kroyer. (71) p. 79, pi. vii, fig. 5 a-c. 



1894. Caligus isonyx T. Scott. (Ilia) 12th Rept. Fishery Board for 

 Scotland, pt. iii, p. 194. 



1896. Caligus diaphanus Bassett-Sniith. (6) p. 156. 



1900. Caligus diaphanus T. Scott. (112) p. 149, pi. v, figs. 20-25. 



1904. Caligus diaphanus A. Scott. (109) p. 38. 



1906. Caligus diaphanus Norman & T. Scott. (88) p. 206. 



Female. — Carapace suborbicular and equal to about 

 two-fifths of the entire length of the animal, and the 

 width rather greater than the length. Frontal plates 

 large, anterior margin slightly emarginate, lunulas 

 rather small, partly concealed. The free thoracic 

 segment short and narrow ; genital segment sub- 

 cordate and equal to about two-thirds of the length of 

 the carapace, truncated posteriorly, and the postero- 

 lateral corners bluntly rounded. Abdomen composed 

 of two joints, and nearly as long as the genital 

 segment, the end joint small. Caudal rami small. 



Antennules of moderate size. Mandibles slender, 

 elongated, with the end joint incurved and distinctly 

 serrated on the inner margin. The fourth pair of 

 thoracic legs short and stout, the ramus, which is 

 composed of three short joints, has both the first and 

 second joints provided with a stout seta of moderate 

 size on the outer distal angle, while the end joint has 

 three similar apical seta3 ; all the setae plumose and of 

 nearly equal size, except that the inner one is rather 

 longer than the others. Fifth pair minute, and, as in 

 the case of other species, occurring as minute setiferous 

 plates near the postero-lateral corners of the genital 

 segment. Length about 4*5 mm. 



Male. — The carapace of the male is rather wider in 

 proportion to its length ; the genital segment is small 

 and scarcely twice the width of the abdomen, it 

 becomes narrower towards the proximal end, and the 

 postero-lateral corners are somewhat angular. The 



