KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 22. N:0 7. 285 



»Affinis ha;c species 1) Onisco Cicadfe Oth. Fabricii, a quo tainen differt capitis pedumque 

 forma, colore et magnitudine; 



2) Onisco Mediisarum O. Fabricii, cuius tameu oculi lineares, arcuati, coerulei, lateribus 

 frontis innati, niniis discrepant. Cum hac utraque Gammarus Libellula peculiare genus constituat, 

 in familias huius descriptione raonographica arctius definiendum. 



Unicura huius animalculi specimen die vicesimo nono mensis lunii anni pra^terlapsi accepi 

 vivum e mari prope Insulam lan Meyen protractum, plura autem mense insequente mortua in 

 stomacho Procellarite glacialis reperi, integra quidem et digestione vix lassa, nisi quod pedum 

 subtilissima pubes detrita esset. 



Inter hfec iuvenilia quoque, dimidife reliquornm magnitudinis, cffiterum simillima illis.» 



The new species of Mandt and Lichtenstein was however forgotten for many 

 years by carcinologists until A. GoÉs iu 1865 restituted it as Themisto libellula, Mandt. 

 During the interval the species bad received new names, as in 1838, Themisto arctica, 

 Kroeyer, and Th. crassicornis, Kroeyer, and as early as in 1835 it bad been identified witb 

 GuÉRiNs Themisto Gaudichaudii, tbereby being for tbe first time placed in the genus to 

 which it really belonged. In 1887 I proposed tbe name Euthemisto Nordenskiöldi for 

 animals whicb I after furtber researcbes bave found to be only younger and less developed 

 specimens of Euthemisto libellula; the characteristics on which the supposed new spe- 

 cies was founded have proved to be of no specific value, as they change witb the growth 

 of tbe animal; thus for instance tbe head is mucb larger in tbe young than in the adult 

 animal, tbe carpal process of tbe second pair of peraeopoda is sboiier, and not only tbe 

 lengtb, but also tbe sbape of tbe fifth pair, changes witb tbe age. 



Owing to its size the adult animal is one of tbe giants of tbe group, being inferior 

 only to some species of Thaumatops, and, if lengtb be considered, also to Xiphocephalus 

 armatus. Some of the species of Lanceola approach tbe extreme lengtb of Euthemisto 

 libellula. Tbe females seein to attain a greater size than the males. The largest male 

 I have examined measured 35 mm. in lengtb from the front margin of tbe bead to tbe 

 apex of tbe last pair of uropoda. The development of the fifth pair of perteopoda is 

 liable to great individual variation, and tbis not always in strict relation to tbe size of 

 tbe animal, so that we may find large individuals, females as well as males, witb tbis 

 pair comparatively short, and only a little longer than tbe next; but on tbe other hand 

 tbe characteristic features of the fifth pair are at once recognizable, namely the breadtb 

 of the femur, tbe elongated tibial process, tbe strongly developed carpus, and tbe bundle 

 of spine-like teeth on tbe front margin of the dactylus; these features are so constant 

 that we find tbem even in young ones, a fcAv days or even one day old. This is the 

 reason also wby I have raaintained tbe generic distinction between Euthemisto and 

 Parathemisto. The carpal process of tbe second pair is somewhat shorter in young 

 specimens than in tbe adult, but even in tbe very young it is always more than balf as 

 long as tbe bind margin of tbe metacarpus. 



