24 
dannet til en kraftig tilspidset og svagt krummet Endeklo. 
Begge disse Bod par er temmelig rigeligt besatte med korte 
Borster. 
Gjellernes Antal er (se Pig. 21) 5 paa liver Side, 
svarende til de 5 Par Fodder. I sin Bygning og Udseende 
viser de intet ussedvanligt. 
Bagkroppens Svommevedlueng (Fig. 24 — 25) er kraftigt 
udviklede og rettede noget skraat udad til Siderne, saa at 
deres ydre Del viser sig, naar Dyret sees ovenfra (Fig. 1), 
ragende frem til liver Side. De bestaar af en sardeles tyk 
og nmskulps Roddel eller Stainme, til livis Ende er ind- 
leddet 2 uligestore Grener. Den ydre af disse er storst, 
dannende en langs Kanterne tet borstebesat, lancetformig 
Plade af Stammens dobbelte Ltengde. Den indre Gren er 
neppe mere end kalvt saa lang, paa lste Par uleddet. paa 
de ovrige bestaaende af to tydelige Segmenter. Paa de to 
forreste Par er denne Gren noget ulige hos begge Kjon. 
Hos Hunnerne er den paa lste Par (Fig. 24) af elliptisk 
Form, men noget vreden, saa at den vanskeligt kan ud- 
bredes i samme Plan. Hos Hannerne er den (Fig. 26) 
derimod tydelig indknebet paa Midten og noget udvidet i 
liver Ende, saint her forsynet med lange og stive, ncilierede 
Borster. Paa 2det Par er denne Gren hos Hunnerne (Fig. 
25) fuldkommen af samme Udseende som paa de folgende, 
bestaaende af 2 med binanden knseformigt forbundne Seg- 
menter, bvoraf det yderste er kengst Og smalt laucetformigt. 
Hos Hannerne har den (Fig. 27) et temmelig afvigende 
Udseende. Den bestaar vistnok ogsaa her af 2 Segmenter, 
men det yderste er her tvedelt eller gaar ud i to ulige 
lange. med standee Borster besatte Dapper. 
Det midterste Halevedhseng (Fig. 28), der egentlig 
forestiller Bagkroppens sidste Segment, er af smal, lancet- 
dannet Form og oventil langs ad Midten noget udhulet, 
med to stumpe Sidekjoler, bvoraf enbver bag Midten haever 
sig til 2 skarpe tornformige Eortsatser. Enden er udtrukket 
til en triangulmr Spids, og til liver Side af denne er ind- 
leddet en kort Torn. Langs ad Sidekanterne af Yedlisenget 
findes desuden en teet Bad af Fjserborster. 
De ydre Halevedhmng (Fig. 28), der sammen med 
det midterste danner den saakaldte Halevifte, bestaar af 
en kort, paa Ydersiden i en stserk tornformig Fortsats 
udgaaende Boddel og to omtrent lige lange pladeformige 
Grene. Den ydre af disse er noget bredere end den indre 
og bar den ydre Kant glat samt lobende bagtil ud i en 
stserk Torn, livorfra en tydelig Sutur strsekker sig paaskraa 
tvsersover Pladens ydre Del. Kanterne er forpvrigt paa 
begge Grener forsynede med en regelnuessig Bad af korte 
Fjserborster. Den ovre Flade er paa den ydre Gren for- 
synet med to, paa den indre med en enkelt stump Lamgdekjol. 
Farven er i levende Tilstand overall rpdlig brun. som 
larger than the 5th. The last segment is transformed into 
a strong, pointed, and slightly curved terminal claw. Both 
these pairs of legs are rather- closely beset with short 
bristles. 
The branchiae (see fig. 21) are 5 in number on either 
side, corresponding to the 5 pa irs of feet. In their structure 
and appearance they exhibit nothing uncommon. 
The natatory appendages of the abdomen (figs. 24, 
25) are powerfully developed and directed somewhat obliquely 
sideways; hence, their exterior part appears, when the 
animal is viewed from above (fig. 1). to project out from 
either side. They consist of an exceedingly thick and 
muscular basal portion, or stem, to the end of which are 
jointed in 2 branches of unequal size. The outer branch is 
the larger, constituting a lanceolate plate, twice the length 
of the stem, and thickly beset with bristles along the edges. 
The inner branch is scarcely half as long; on the 1st pair 
it has no articulations, on the others it consists of two 
distinct segments. On the 2 foremost pairs, this branch 
differs somewhat in the 2 sexes. In the females, it has on 
the 1st pair (fig. 24) an elliptic form, but is somewhat twisted, 
so as with difficulty to admit of being spread out in the 
same plane. In the males, on the other hand, it is (fig. 
26) distinctly constricted in the middle, and somewhat ex- 
panded at either extremity, as also furnished with long and 
stiff unciliated bristles. On the 2nd pair, this branch is 
in the females (fig. 25) of precisely the same appearance 
as on those succeeding it, consisting as it does of 2 con- 
nected geniculate segments, of which the outer one is the 
longer, and narrow lanceolate. In the males, it exhibits 
(fig. 27) a rather different appearance. True, it consists 
of 2 segments; but the outer one is bipartite, or protends 
in 2 lobes of unequal length, beset with strong bristles, 
The telson (fig. 28). that strictly represents the last 
segment of the abdomen, is slender, lanceolate in form, 
and somewhat hollowed out above, along the middle part, 
with two obtuse lateral carinse, each of which, posterior to 
the middle, rises as an acute spiniform probation. The 
extremity is drawn out to a sharp triangular point, on 
either side of which is jointed in a short spine. Extending 
along the lateral borders of the appendage, occur moreover 
a close-set series of plumose bristles. 
The exterior caudal appendices or uropoda (fig. 29), 
which, together with the telson, form the so-called caudal 
fan. consist of a short basal part, produced on the outer 
side as a strong spiniform prolation, and of two lamellar 
branches about equal in length. The outer of these 
branches is somewhat broader than the inner, with the 
exterior margin smooth and projecting posteriorly as a 
powerful spine, whence a distinct suture passes obliquely 
straight across the outer portion of the plate. For the 
rest, the borders of both branches are furnished with a 
regular series of short plumose bristles. On the upper 
surface of the outer branch occur two obtuse, longitudinal 
carinm, on that of the inner a single one. 
Colour in a living state everywhere reddish-brown, as 
