36 EEV. T. E. E. STEBBING— BISCATAN PLANKTOIV : 



There still remain some species of Hyperia in which the mandihles have been 

 definitely described for the male only, so that a subdivision of the genus dependent on 

 the mandibular character in the two sexes cannot for the moment be completely carried 

 out. 



It should be borne in mind that in Myperioides longipes, though the fifth joint is 

 produced in both pairs of gnathopods, it is less so in the first than in the second. The 

 elongate third and fourth perseopods have the fourth joint shorter than the fifth, but in 

 the shorter fifth pair the fifth joint is a little shorter than the fourth. The third uropods 

 have a striking appearance by reason of the deep denticulate emargination at the upper 

 part of the inner border in the outer ramus, which is rather longer than the inner one. 

 This character becomes more conspicuous in proportion to the size of the specimen. The 

 almost semicircular telson can scarcely be relied on as furnishing a permanent generic 

 character, since JSyperla Fahrei, Milne-Edwards, has a completely similar telson, while 

 other species of the genus have the telson triangular. 



The length of measured specimens varied from 2*5 mm. to a little over 5 mm., none 

 attaining the length of 6 mm. assigned by Chevreux and Vosseler to full-grown males. 



This species was obtained in the Bay of Biscay in no less than thirty-two hauls. 

 There were several males with numerously -jointed antennge, but none in which the 

 flagellar joints had attained the elongate tenuity characteristic of complete development. 

 The great majority of the specimens were obtained by hauls between the surface and 

 100 fathoms. The occurrences are discussed on p. 49. 



Parathemisto, Boeck, 1871. 



1871. Pai-athemisto, Boeck, Vid.-Selsk. Forhandlinger (Cliristiauia) for 1870, p. 87 (7). 



1889. Farathemisto, Bovallius, K. SvcDsk. A^et.-Akad. Handliugar, Bd. xxii. No. 7, p. 248. 



1890. Farathemisto, Sars, Crustacea of Norway, vol. i. p. 10. 



1901. Farathemisto, Vosseler, Amphipoden der Plankton-Exp. p. 80. 



The dilated and more or less ovoid fifth joint of the first and second perseopods, by 

 which in adults the species of this genus and of Euthemisto are so readily distinguished 

 from Hyperia, does not attain its characteristic shape in very young specimens. 



19. Parathemisto oblivia (Kroyer). 



1838. Hyperia oblivia, Kroyer, Gronlands Amfipoder, Danske Selsk. A£h. pt. vii. p. 298, pi. 4. fig. 19. 

 1871. Parathemisto abyssorum, Boeck, Vid.-Selsk. Forhandlinger (Christiania) for 1870, p. 87 (7). 

 1889. Farathemisto oblivia, Bovallius, K. Svenska Vet.-Akad. Handlingar, Bd. xxii. No. 7, p. 251, 



pi. 12, figs. 11-16, and figures in text. 

 1896. Farathemisto oblivia, Bonnier, Ann. Univ. Lyon, Campagne du 'Caudan,' p. 611, pi. 35. fig. 1. 

 1898. Parathemisto abyssorum. Fowler, Proc. Zool. Soc. London, p. 583. 

 ]901. Parathemisto oblivia (?), Vosseler, Amphipoden der Plaukton-Exp. p. 80, pi. 7. figs. 31-25, 



pi. 8. figs. 1, 2. 

 Without giving all the references, it may suEBce here to say that the identification of 

 Boeck's P. abyssorum with Kroyer's species was suggested as probable by H. J. Hansen 

 in 1887, accepted by Bovallius in 1889, Sars in 1890, and Chevreux in 1900. The 



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