85 



or as I. pelayica of Leach. The latter mistake has hecn previously committed by 

 the present author; but after having become acquainted with the true /. pelagica 

 Leach. I now find that it is a very different species, exhibiting a much closer 

 relationship to I. emarginata,. From this species, however, it is at once distin- 

 guished by the very different form of the last segment of the metasome. in which 

 respect it also differs conspicuously from the North American /. phosphor ea. 



Occurrence. The species occurs along the whole Norwegian coast, from 

 the Christiania Fjord to Vadsd. and is often found in great abundance among 

 decaying alga?, in depths ranging from 6 to 20 fathoms. As to its distribution 

 out of Norway, it is impossible at present to state anything with certainty; but 

 it is most likely that it also occurs at any rate off the British Isles and in the 

 Kattegat. 



6. Idothea emarginata (Fain-.). 



(PI. XXXV, fig. 2.) 

 Cymothoa emarginata, Fabricius. Entom. Syst. II, p. 508. 



Syn: IdotJica extisa, Bosq. 

 oestrum, Pennant. 



Specific Characters. Body oblong oval, scarcely 3 times as long as it is 

 broad, and much larger in male than in female. Coxa! plates in female rather 

 small and not contiguous, in male much larger, and forming on each side a broad 

 marginal area. Last segment of metasome abruptly truncated at the tip, hind 

 edge slightly emarginated, with the lateral corners distinctly projecting. Eyes and 

 superior antennae about as in I. neylecta. Inferior antenna; somewhat less slender, 

 scarcely reaching to the end of the 2nd segment of mesosome, flagellum not much 

 longer than the peduncle, and composed of from 12 to 1(5 articulations. Legs 

 about as in /. neglccta. Stylet of 2nd pair of pleopoda in male somewhat longer 

 than in /. neglccta, though not reaching to the end of the inner plate. Uropoda 

 with the terminal piece slightly emarginated at the tip. Colour rather variable, 

 sometimes uniformly dark brown, sometimes variegated with larger whitish patches, 

 which are often confluent along the sides, so as to leave the marginal area?, formed 

 by the coxal plates, uncoloured. Length of adult female 18 mm., of male 30 mm. 



Remarks. This species was recorded as early as in the year 1793 by 

 Fabricius, as Cymothoa emarginata. By earlier British authors (Pennant and 

 Leach) it was named Idothea oestrum. Though very nearly allied to I. neglecta, 

 this form is readily distinguished, both from that species and the other Norwegian 

 Idothese, by the abruptly truncated and emarginated terminal segment of the meta- 

 some, for which reason it has never been confounded with any of the other species. 



