110 
Den er (se Pig. 28), i Modsmtning til livacl Tilfaddet er 
hos Slsegten Arcturus, alene indskramkct til 4de Forkrops- 
segment og dannes af 2 fra dettes Yentralside udgaaende 
brede, valvelformige, i Midton sammenstodende Klapper, 
indenfor hvilke de talrige vEg bar sin Plads. 
Bagkroppens Lemmer stemmer i alt vaesentligt fuld- 
kommen overens med samme bos foregaaende Slsegt. 
Beskrivelse af Hannen. Don fuldt udviklede oiler 
skegtsmodne Han (Pig. 32) riser et fra Hunnen meget af- 
vigende Udseende, idet Legemet er betydelig spinklere. 
Navnlig gjslder dette 4de Forkropssegment, der er over- 
ordentlig smalt, regelmsessigt cylindriskt og kjondoligt lsen- 
gerc* end dot bagenfor liggeude Af'snit af Legemet. 
Af Leiumerne er det alene lste Par Fplere og de 2 
forreste Par Bagkropslemmer, der viser nogen udpr.egct 
Forskjel fra samme hos Hunnen. 
lste Par Folere (Pig. 33) er forholdsvis storre end 
hos Hunnen og har navnlig Svoben stserkere udviklet og 
af samme Lsengde som hole Skaftet. Ligeledes er de til 
samme faestede Sandsevedhseng tilstede i et betydelig 
storre Antal, nemlig 13. 
De til Yentralsiden af sidste Porkropssegment fae- 
stede ydre Kjonsvedlueg har (se Pig. 34) Pormen af 2 
cylindriske, fra en hellos Basis udgaaende og med smaa 
Pigge besatte Fortsatser, der er retted© bagtil mellem Ro- 
den af ltse Par Bagkropslemmer. Indenfor den hellos 
Basis sees tydeligt de 2 convergerende rasa deferentia, der 
begiver sig hvert ind i den tilsvarende Fortsats og ender 
med en fin Aabniug paa den stumpe Spids af samme. 
lste Par Bagkropslemmer (Fig. 34) udmserker sig 
derved, at den ydre Plade viser en eiendommelig Boining 
ved Basis, samt derved, at den indre Plade nrer Roden 
har i den ydre Kant en Udstaaenhed, hvortil 3 strerke 
ncilierede Borster er fsestede. 
Endnu mere afvigende er 2det Par (Pig. 35). Den 
ydre Plade er nemlig her forsynet med et temmelig stort 
koniskt tilspidset og med 2 stive Borster endende Yed- 
haeng, der er fsestet til en stserk Afsats i den ydre Kant 
lifer Basis. Dette Par synes herved ved forste 0iekast at 
bsere 3 Endeplader. 
Begge disse Par Lemmers eiendommelige Bygning 
staar aabenbart i et bestemt Porhold til Copnlationsakten, 
og vi trseffer ogsaa lignende Indretninger hos andre Iso- 
podehanner. 
Parven saavel hos Han som Hun er ensformig lvs 
graagul, uden morkere Shatteringer. 
Lsengden af Hunnen er 14 ram . Hannen er noget 
lsengere. 
Forekomst og Udbredning. Exemplarer af den 
ovenfor beskrevne Art er indsamlede paa 5 for.skjellige 
Stationer, livoraf de 4 ligger langs med det vestlige Af- 
held fra vore Havbanker fra Hoiden af Romsdalen til 
Hoiden af Nordkap, den 5te (Stat. 48) i Havet 0st af 
ture. Contrary to what is the case in the genus Arctu- 
rus, it is exclusively confined to the 4th pedigerous seg- 
ment, and composed of 2 broad valvular flaps, proceeding 
from its ventral side and meeting in the middle, within 
which the numerous eggs are deposited. 
The abdominal limbs agree perfectly in all essential 
characteristics with those in the preceding genus. 
Description, of the Male. — The full-grown or sex- 
ually mature male (fig. 32) presents an appearance very 
different from that of the female, the body being much 
more slender. This applies more particularly to the 4th 
segment, which is exceedingly narrow, regular -cylindric. 
and obviously longer than the succeeding section of the body. 
Of the appendages, it is the 1st pair of antennae 
only, and the 2 foremost pairs of pleopoda that exhibit 
any considerable difference from those in the female. 
The 1st pair of antennae (fig. 33) are relatively lar- 
ger than in the female, having in particular the flagellum 
more fully developed, and equal in length to the whole 
peduncle. Moreover, the sensory .appendices attached to 
the latter are present in a much greater number, — viz. 13. 
The outer sexual appendages attached to the ventral 
side of the last pedigerous segment, have the form (see 
fig. 34) ot 2 cylindrical projections, issuing from a com- 
mon base and beset with minute spikes, the sa.id pro- 
jections extending backward between the bases of the 1st 
pair of pleopoda. Within the common base, are distinctly 
seen the 2 converging vasa deferentia, each of which en- 
ters the corresponding projection, and terminates in a mi- 
nute orifice on its obtuse point. 
The 1st pair of pleopoda (fig. 34) are characterized 
by the outer plate exhibiting a peculiar bend at the base, 
as also by the inner plate having, in proximity to the 
base, on the outer border, a protuberance, to which are 
attached 3 strong non-ciliated bristles. 
Still greater is the divergence of the 2nd pair (fig. 
35). The outer plate, namely, is here furnished with a 
rather large, conically pointed appendix, terminating in 2 
stiff bristles, attached to a strong lodge on the outer 
margin, near the base. This pair acquire thereby, at the 
first glance, the appearance of bearing 3 terminal plates. 
The peculiar structure of both these pairs of pleo- 
poda must obviously stand in some relation to the act of 
copulation; indeed, something similar is met with in other 
Isopod males. 
Colour, both in the male and female, a uniform light 
greyish-yellow, without any darker shades. 
Length of the female .14”"" : the male is a trifle 
longer. 
Occurrence and Distribution. — Specimens of the 
species described above were collected at 5 different Sta- 
tions, 4 located along the western slope of the outer Nor- 
wegian banks, extending from Romsdalen to the North 
Cape, the 5th (Stat. 48) in the open sea, east of Iceland; 
