70 
har sin Plads. Bag Nakkefuren begynder den frie 
Del af Rygskjoldet, der som en Kappe lost bedek- 
ker den underliggende Krop. Denne Del har efter 
Midten en tydelig Kjol, der bliver mere fremtre- 
dende bagtil, hvor den ender med et spidst Frem- 
spring i Bunden af Rygskjoldets bagre Indsnit. 
Fortil er, som ovenfor anfort, Rygskjoldet fuldkom- 
men sammenvoxet med Hovedet og danner her ne- 
dentil {se Fig. 2) en halvmaaneformig horizontal Du- 
plicatur, hvorved Hovedet faar en udpreget, bredt 
skovldannet Form (se ogsaa Fig. 3). Hvad angaar 
Rygskjoldets finere Bygning, saa mangler det ethvert 
Spor af Kalkafleiringer og er derfor meget boieligt 
og idethele af en temmelig blod Consistens. Det 
er, som seedvanligt, sammensat af 2 Lameller, en 
ydre meget tynd, fuldkommen glat og glindsende 
Lamelle af chitinos Beskaffenhed, og en indre mem- 
branos og noget spongios Lamelle. Mellem begge 
findes et System af Hulrum, hvori Blodet cirkulerer, 
og desuden de 2 meget sterkt udviklede Skal- 
kjertler.. Disse er delvis udvendigt synlige som 
aflangt ovale, noget sabelformigt krummede Felter, 
der fra Nakkefuren strekker sig langs ad Siderne 
af den frie Del af Rygskjoldet (se Fig. 3). De be- 
staar hver (se Tab. XIII, Fig. 4) af en flere Gange 
slyngeformigt bugtet Kanal, der synes at udmunde 
ved Basis af Kindbakkerne. 
Borttager man den frie Del af Rygskjoldet, sees 
(Tab. XIU, Fig. 1 og 2) den underliggende Krop at 
vere delt i en Rekke meget ensformige Segmenter, 
der ikke. grupperer sig til tydeligt markerede Af- 
snit, om det end efter Forholdet af Lemmerne lader 
sig gjore med nogenlunde Sikkerhed at bestemme 
Grendserne for de 3 sedvanlige Kropsafsnit: Midt- 
krop, Bagkrop og Hale. Segmenternes Antal er ialt 
28. Heraf tilhorer de 11 forste Midtkroppen og 
berer hvert et enkelt Par Fodder, hvorimod de 11 
folgende, til Bagkroppen horende Segmenter beer 
hvert flere Par Fodder. De 6 bagerste Segmenter 
er fodlose og representerer derfor den egentlige 
Hale. De er meget skarpt begreendsede, med Bag- 
kanten noget hevet og rundt om bevebnet med 
korte Tagger, der ogsaa forefindes paa Rygsiden af 
de nermest tilgreendsende Segmenter af det fore- 
gaaende Afsnit. Sidste Halesegment (se Tab. XII, 
Fig. 23--27) er noget lengere end de foregaaende, 
og har oventil paa hver Side af Midtlinien en rund- 
agtig Knude besat med en Kreds af smaa Tagger, 
i hvis Midte en fin Sandseborste sees at rage frem 
(se Fig. 28). Ved Enden af Segmentet findes paa 
den ventrale Side Analaabningen, og umiddelbart 
over denne fortsetter Segmentet sig i en tynd ho- 
rizontal Plade, der skyder frem bagtil mellem Basis 
at de 2 Haletraade. 
rounded prominence, upon which the 2 compound 
eyes are situated. Behind the cervical furrow, 
the free portion of the carapace begins, covering 
loosely, like a mantle, the underlying body. 
Down the centre of this part, there is a distinct 
keel, which becomes more prominent posteriorly, 
and ends in a sharp projection at the bottom 
of the posterior emargination of thé carapace. As 
stated above, the carapace is completely coalesced 
in front with the head, and there forms, below 
(see fig. 2), a crescent-shaped horizontal duplicature, 
whereby the head: acquires a pronounced shovel- 
like shape (see also fig. 3). With regard to the 
finer structure of the carapace, no trace what- 
ever of calcareous deposit is found in it, and it is 
therefore very flexible and, on the whole, of a rather 
soft consistence. It is, as usual, composed of two 
lamella, one .external, very thin, perfectly smooth 
and shining, and of a chitinous nature, the other, 
an inner, membranous and somewhat spongy lamella. 
Between the two there is a system of cavities, 
through which the blood circulates, and also 2 very 
highly developed shell glands. These are partially 
visible externally in the form of long oval, rather 
ensiformly curved areas, extending from the cervical 
suleus along the sides of the free portion of the 
carapace (see fig. 3) They each consist (see Pl. XIII, 
fig. 4) of a tube with several windings, which seems 
to open at the base of the mandibles. 
If the free portion of the carapace be removed 
(Pl. XII, figs. 1, 2), the underlying body is found 
to be divided into a series of very uniform segments, 
which do not apportion themselves into distinctly 
marked sections, although it is possible, by the rela- 
tions of the limbs to one another to determine, with 
a measure of certainty, the limits of the 3 ordinary 
divisions of the body, — the mesosome, the meta- 
some and the tail. The number of the segments is 
28 in all. Of these the first 11 belong to the meso- 
some, and each carry one pair of legs, whereas the 
following 11 segments, which belong to the meta- 
some, each carry several pairs of legs. The last 
6 segments have no legs, and therefore represent 
the tail proper. They are very sharply defined, the 
posterior edge being somewhat raised, and armed 
all round with short denticles, which are also found 
on the dorsal side of the adjacent segments of the 
preceding section. The last caudal segment (see Pl. 
XII, figs. 23—27) is rather longer than the prece- 
ding ones, and has above, on each side of the me- 
dian line, a round prominence surrounded by a circle 
of small denticles, from the midst of which a fine 
sensory bristle is seen to project (see fig. 28). At 
the end of the segment, on the ventral side, is the 
anal orifice, and immediately above it, the segment 
is prolonged into a thin horizontal lamella, protru- 
——_— —" 
