74 BRITISH PARASITIC COPEPODA. 



an oval form, not much longer than, and about twice the 

 width of, the following segments ; its distal margin is 

 rounded, with a minute setiferous plate on each side 

 representing the fifth pair of legs. Abdomen com- 

 posed of two subequal but indistinctly segmented 

 joints. Length about 4*5 mm. 



Habitat. — Found for the most part on lythe, G-adus 

 pollachius, adhering to the inside of the mouth, and 

 rarely on other fishes. Plymouth (Bassett- Smith). 

 Falmouth [A. M. Norman). On salmon captured at 

 Polperro, Cornwall (Laughrin in 'Museum Xormania- 

 num'). (rirvan, Firth of Clyde, and at Aberdeen Fish- 

 Market (T. Scott). Irish Sea (A. Scott). 



This species does not appear to be so common as some of 

 the others. 



7. Lepeophtheirus sturionis (Kroyer). 

 (Plate XVIII, figs. 16-19 ; Plate XXI, fig. 1.) 



1837. C aligns sturionis Kroyer. (70) pi. vi, fig. 6. 



1840. Lepeophtheirus sturionis M. Edwards. (43) vol. iii, p. 457. 



1863. Lepeophtheirus sturionis Kroyer. (71) p. 139, pi. xvii, fig. 4. 



1905. Lepeophtheirus sturionis T. Scott. (116) p. 110, pi. v, figs. 7-14. 



Female. — Carapace suborbicular and equal to about 

 two-fifths of the entire length of the animal. Frontal 

 plates not very prominent. Free thoracic segment 

 not very clearly defined. Genital segment somewhat 

 pyriform, widest posteriorly, becoming gradually 

 narrower towards the front, then suddenly contract- 

 ing to about the width of the free thoracic segment, 

 length about equal to the width at the posterior end, 

 and to about two-thirds of the length of the carapace; 

 bluntly rounded at the postero-lateral corners. Ab- 

 domen tolerably elongated and narrow, being nearly 

 three-fourths as long as the genital segment, slightly 

 constricted near the distal end, the constriction forming 

 a kind of false joint. Caudal rami very short and 

 somewhat rudimentary. 



Basal joint of the antennules tolerably expanded. 

 Antennse robust, and armed with large and strong 



