KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 22. N:0 7. 279 



against the anterior margin of the carpus: fourth and fifth pairs subequal, of the same form as 

 the third, but not more than half the length. Three posterior pairs of pleopoda subequal, the 

 last being the longest; rami double, lanceolate. Telson small, squamose.» 



In 1868 Spence Bate and Westwood repeated essentially the same diagnosis. 

 In 1870 A. Bobck gave the following diagnosis, which he repeated in 1872: 



»Instrumenta cibaria et pedes lmi et 2di paris agqve ut apud genus antecedens (Parathe- 

 misto). Pedes 3tii et 4ti paris articulo 3tio brevissimo; articulo 4to perdilatato, in margine po- 

 steriore spinoso et manu qvodammodo formanti ; articulo 5to et 6to junctis ungvem longum 2- 

 articulatum efficientibus. Pedes 5ti paris pedibus 6ti et 7mi paris multo longiores; articulo lmo 

 dilatato, 3tio brevi, 4to et 5to prselongato.w 



In 1872 Claus characterizes the genus as follows: 



»Fiinftes Fusspaar sehr stark verlangert, die beiden vorhergehenden viel ki'irzern Fuss- 

 paare mit zusammegesetzter triangularer Greifhand. Sechstes und siebtes Fusspaar gleich- 

 gestaltet. Caudalgriffel sehr lang und stabformig.» 



In 1875 Schiodte gave an account of the mouth-organs of Euthemisto. 

 In 1887 I corrected the name Themisto into Euthemisto, because the former was 

 found to be preoccupied for a genus of Mollusca. 



The first species belonging to this genus was minutely described in 1822 by M. W. 

 Mandt 1 ) under the name Gammarus Libellula. The second species was the type for the 

 generic name Themisto, Th. Gaudichaudii, founded in 1825 by F. E. Guerin. In 1838 

 Kroeyer described two new species Themisto arctica and Th. crassicornis, which Boeck 

 justly placed as synonyms of Th. libellula, Mandt. The next new specific name was 

 Dana's Themisto antarctica, proposed in 1852. Thereafter follows Th. Guerini, instituted 

 in 1862 by Spence Bate, it is, however, nothing but a young female of Euthemisto 

 antarctica. 



In 1865 Goes instituted the new species Themisto compressa, and in 1870 Boeck 

 gave the diagnosis of Th. bispinosa, n. sp., which is identical with Goes' species. 



In 1879 G. M. Thomson described an Euthemisto which he justly supposed to 

 be E. antarctica, Dana. In 1887 I gave a short description and figures of E. Norden- 

 skibldi, n. sp., which however, as Hansen suggested in the same year, is only a young 

 form of E. libellula. In 1888 Stebbing described the new species E. australis, and 

 E. Thomsoni, which latter in my opinion is identical with E. Gaudichaudii. 



After a close examination of the very rich material at my disposal I am convinced 

 that all these specific names really form only four tolerably good species viz: 



Gammarus Libellula, Mandt, 



Themisto arctica, Kroeyer, I v .-, ■ , vu n i tm.., 



, ' . _ ' >= Euthemisto libellula Mandt. 



Themisto crassicornis, Kroeyer, 

 Euthemisto Nordenskibldi, C. Bovallius, 



J ) M. W. Mandt. Observationes in historiam naturalem et anatomiam coraparatam in itinere Groen- 

 landico facte. Dissertatio. (Berlin, 1822), p. 32 — 34. 



