70 



har sin Plads. Bag Nakkefuren begyuder den frie 

 Del af Rvgskjoldet, der som en Kappe lost Ijedæk- 

 ker den underliggende Krop. Denne Del har efter 

 Midten en tydelig Kjol, der bliver mere fremtræ- 

 dende bagtil, hvor den ender med et spidst Frem- 

 spring i Bunden af Eygskjoldets bagre Indsnit. 

 Fertil er, som ovenfor anført, Rygskjoldet fuldkom- 

 men samnienvoxet med Hovedet og danner her ne- 

 dentil (se Fig. 2) en halvmaaneformig horizontal Du- 

 plicatur, hvorved Hovedet faar en udpræget, bredt 

 skovldannet Form (se ogsaa Fig. 3). Hvad angaar 

 Rygskjoldets finere Bygning, saa mangler det ethvert 

 Spor af Kalkaileiringer og er derfor meget bøieligt 

 og idethele af en temmelig blød Consistens. Det 

 er, som sædvanligt, sammensat af 2 Lameller, en 

 ydre meget tynd, fuldkommen glat og glindsende 

 Lamelle af chitinøs Beskaftenhed, og en indre mem- 

 branes og noget spongios Lamelle. Mellem begge 

 tindes et System af Hulrum, .hvori Blodet eirkulerer, 

 og desuden de 2 meget stærkt udviklede Skal- 

 kjertler. Disse er delvis udvendigt synlige som 

 aflangt ovale, noget sabelformigt krummede Felter, 

 der fra Nakkefuren strækker sig langs ad Siderne 

 af den frie Del af Rygskjoldet (se Fig. 'å). 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. XIII, Fig. 1 og 2) den underliggende Krop at 

 være delt i en Række 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 

 (irændserne for de 3 sædvanlige Kropsafsnit: Midt- 

 krop, Bagkrop og Hale. Segmenternes Antal er ialt 

 2S. Heraf tilhører de 11 forste Midtkroppen og 

 liærer hvert et enkelt Par Fodder, hvorimod de 11 

 folgende, til Bagkroppen horende Segmenter bærer 

 hvert flere Par Fødder. De 6 bagerste Segmenter 

 er fodløse og rein^æsenterer derfor den egentlige 

 Hale. De er meget skarpt Ijegrændsede, med Bag- 

 kanten noget hævet og rundt om bevæbnet med 

 korte Tagger, der ogsaa foreiindes paa Rygsiden af 

 <le nærmest tilgrændsende Segmenter af det fore- 

 gaaende Afsnit. Sidste Halesegment (se Tab. XII, 

 Fig. 23 — 27) er noget længere 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 fortsætter Segmentet sig i en tj-nd ho- 

 rizontal Plade, der skyder frem !)agtil mellem Basis 

 at de 2 Haletraade. 



rounded prominence, upon wliieh tlie 2 compound 

 eves are situated. Behind the cervical furrow, 

 the free portion of the carapace begins, covering 

 loosely, like a mantle, the underlj-ing body. 

 Down the centre of this part, there is a distinct 

 keel, which becomes more prominent posteriorly, 

 and ends in a .sharp projection at tlie bottom 

 of the posterior emargination of the cara]jace. As 

 stated above, the carapace is completely coalesced 

 in front with the head, and there forms, below 

 (see fig. 2), a cre.scent-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 

 lamellæ, one external, very thin, perfectly smooth 

 and shining, and of a chitinous nature, the other, 

 an inner, membranous and somewhat spong}^ 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 

 siilcus along the .sides of the free portion of the 

 carapace (see fig. 3) They each consist (see PI. XIII, 

 fig. 4) of a tube with several windings, which seems 

 to open at the l^ase of the mandibles. 



If tlie free portion of the carapace be removed 

 (PL XIII, figs. 1, 2), the underlying body is found 

 to be divided into a series of very imiform 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 certaintj', the limits of the 3 ordinary 

 divisions of the body, — the mesosome, the meta- 

 some and the tail. The niimber 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 projjer. 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 PI. 

 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 cii'cle 

 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 himella, protru- 



