21 



sidste er fæstet 4 stærke Torner, og fra Spidsen 

 udgaar 2 lignende, hvoraf den inderste er længst. 

 Imellem Tornerne lindes ogsaa her fine udadrettede 

 Børster, medens Berstei'ne i Inderkanten er stærkt 

 reducerede. 



Halegrenene (Fig. 12) er omtrent saa lange som 

 de 2 sidste Bagkropssegmenter tilsammen og ialniin- 

 deligbed stærkt divergerende. De er af smal lineær 

 Form, ganske lidt afsmalnende mod Enden og 

 rundtom for.synede med en Rad af korte ucilierede 

 Torner, der ved Spidsen antager Formen af stærkt 

 forlængede Borster. Foruden disse lindes langs 

 Inderkanten en Rad af betydelig længere og finere, 

 tæt cilierede Borster. 



Dj'rets Farve er noget varierende fra meget 

 bleg gulagtig til temmelig intens rødbrun. De mest 

 udpræget farvede Exemplarer har jeg observeret i 

 vor arktiske Region. 



Beskrivelse af den slægtsmodne Han. 



Medens den endnii ikke slægtsmodne, skjondt 

 forøvrigt fuldt udvoxede Hau (se Tab. II, Fig. 1) 

 kun lidet skiller sig i sit Udseende fra Hunnen, er 

 Forskjellen mellem de to Kjøn i den slægtsmodne 

 Tilstand saa skarpt udpræget (se Tab. I, Fig. 1 og 

 3), at man uden en noiere Undersogelse knapt en- 

 gang skulde tro, at de tilhørte samme Art. Kjons- 

 forskjellen er udtrykt saavel i den hele Habitus 

 som i Structuren af enkelte af Lemmerne, især de 

 2 Par Følere, der er modificerede paa en meget lig- 

 nende Maade som hos Hannerne af de fleste Ampbi- 

 poder. 



De største Hanner, jeg har fundet, liavde en 

 Længde af omtrent 12 mm.; men jeg har ved vor 

 Sydkyst truftet Hanner af knapt mere end den halve 

 Størrelse, skjøndt fuldstændigt slægtsmodent ud- 

 viklede. 



Legemets Form er (se Tab. I, Fig. 3) paafaldende 

 smækrere end hos Hunnen, og navnlig er Rygskjol- 

 det kjendelig smalere, seet fra Siden af elliptisk 

 Form, med Hoiden neppe halvt saa stor som Læng- 

 den. Fremdeles er Bagkroppen noget længere i 

 Forhold til Forkrop])en, og dens forreste Afsnit 

 kraftigere udviklet end iios Hunnen. Endelig giver 

 de enormt forlængede Halegrene Dyret et fra Hun- 

 nen meget afvigende Udseende. 



Øinene er fuldkommen af samme Bygning som 

 hos Hunnen, men synes noget større og har det 

 ydre Parti stærkere udvidet. 



single oval joint whose inner edge is straight, 

 whilst the outer edge is somewhat curved. To the 

 last named 4 strong spines are secured, and 2 simi- 

 lar ones issue from the point, of which the inner- 

 most one is the longest. Between the spines there 

 are also found here fine bristles directed outwards, 

 whilst the bristles on the inner margin are greatly 

 reduced. 



The caudal rami (fig. 12) are about same 

 length as the two last posterior segments of the 

 bodj^ taken together, and are usually strongly diver- 

 gent. They are of narrow, linear form, quite slightly 

 narrowed towards the extremity, and furnished 

 roundabout with a series of short non-ciliated spines, 

 which at the tip assume the form of greatU' ])ro- 

 longed bristles. Besides these there are found, along 

 the inner edge, a series of considerably longer and 

 finer, closely ciliated bristles. 



The colour of the animal is somewhat variable, 

 from very pale yellowish to pretty intense red- 

 brown. I have observed the most distinguished co- 

 loured specimens in the Norwegian Arctic region. 



Description of the sexually ripe male. 



Whilst the not j^et sexuallj^ ripe male, al- 

 though in other respects fully developed (see PI 

 II, fig. 1), distinguishes itself in appearance only 

 slightly from the female, the dilference between the 

 two sexes in the sexually ripe condition is so 

 sharply defined (see PI. I, fig. 1 and 3), that without 

 a close examination the observer would scarcely 

 even believe that they pertained to the same species. 

 The sexual diiference is expressed both by the en- 

 tire habitus, as well as in the structure of some of 

 the appendages, especially the two pairs of antennæ, 

 which are modified in a very similar manner to 

 that of the males of most Amphi])ods. 



The largest males I have found had a length 

 of about 12 mm ; but on our south coast I have met 

 with males of scarcely more than half the size, 

 although completely sexually developed. 



The form of the body (see PI. I. fig. 3) is con- 

 spicuously more slender than in the female, and the 

 carapace, especially, is perceptibly narrower; viewed 

 from the side the shape is elliptical, the height 

 being scarcely half so great as the length. Further, 

 the posterior division of the body is somewhat 

 longer in relation to the a.nterior one, and its fore- 

 most section more powerfully developed than in the 

 female. Finalh', the enormoush^ ju'olonged caudal 

 rami impart to the animal a very different appear- 

 ance from the female. 



The eyes are of exactly the same structure as 

 in the female, but appear to be somewhat larger, 

 and have the outer portion more dilated. 



