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



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

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

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



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

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



»Instrumenta cibaria et pedes Imi et 2di paris ajqve ut apud genus antecedens {Parathe- 

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

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

 articulatum efficientibus. Pedes 5ti paris pedibus 6ti et 7mi paris niulto longiores; articulo Imo 

 dilatato, 3tio brevi, 4to et 5to prajlongato.» 



In 1872 Claus characterizes the genus as follows: 



»Funftes Fusspaar sehr stark verlängert, die beiden vorhergehenden viel kurzern Fuss- 

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

 gestaltet. Caudalgriffel sehr läng und stabförmig.» 



In 1875 ScHi0DTE 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^) under the name Gammarus Lihellula. The second species was the type for the 

 generic name Themisto, Th. Gaudicliaudii, founded in 1825 by F. E. Guérin. In 1838 

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

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

 Dana's Themisto a7itarctica, 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 GoÉs instituted the new species Themisto compressa, and in 1870 Boeck 

 gave the diagnosis of Th. hispinosa, n. sp., which is identical with GoÉs' 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 ^. Norden- 

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

 form of E. lihellula. 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 Lihellula, Mandt, 



Themisto arctica, Kroeyer, U Euthemisto lihellula Mandt. 



Themisto crassicornis, Kroeyer, 

 Euthemisto Nordenskiöldi, C. Bovallius, 



') M. W. Mandt. Observationes in historiam naturalem et anatomiam comparatam in itinere Groen- 

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



