har sin Plads. Bag Nakkefureu begynder den frie 

 Del af Rvgskjoldet, der som en Kappe lost bedæk- 

 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 Rygskj eldets bagre Indsnit. 

 Fortil er, som ovenfor anfort, Rygskjoldet fuldkora- 

 men sammenvoxet med Hovedet og danner her ne- 

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

 plicatur, hvorved Hovedet faar en iidprteget, liredt 

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

 Rygskj oldets finere Bygning, saa mangler det ethvert 

 Spor af Kalkafleiringer og er derfor meget boieligt 

 og idethele af en temmelig l)lod Consistens. Det 

 er, som sædvanligt, sammensat af 2 Lameller, en 

 ydre meget tynå, fuldkommen glat og glindsende 

 Lamelle af chitinøs Beskatfenhed, og en indre raem- 

 branos og noget spongios Lamelle. Mellem begge 

 tindes et System af Hnlrnm, livori Blodet cirknlerer, 

 og desuden de 2 meget stærkt udviklede Skal- 

 kjertler. Disse er delvis udvendigt synlige som 

 aflangt ovale, noget sabelformigt krummede Felter, 

 der fra Xakkefuren strækker sig langs ad Siderne 

 af den frie Del af Rygskjoldet i se Fig. 3). De be- 

 staar hver (se Tab. XIII, Fig. 4) af en Uere (lange 

 slyngeformigt bugtet Kanal, der synes at udmunde 

 ved i^asis 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 Forlioldet af Lemmerne lader 

 .sig gjore med nogenlunde Sikkerhed at bestemme 

 (rrændserne for de 3 sædvanlige Kropsafsnit: Midt- 

 krop, liagkrop og Hale. Segmenternes Antal er ialt 

 28. Heraf tilkorer de 11 forste Midtkroppen og 

 bærer hvert et enkelt Par Fedder, hvorimod de 11 

 folgende, til Bagkroppen horende Segmenter bærer 

 hvert tiere Par Fodder. De 6 bagerste Segmenter 

 er fodlose og rejn-æsenterer derfor den egentlige 

 Hale. De er meget skarpt begrændsede, med Bag- 

 kanten noget hævet og rimdt om bevæbnet med 

 korte Tagger, der ogsaa forefindes paa Rygsiden af 

 de nærmest tilgrændsende Segmenter af det fore- 

 gaaende Afsnit. Sidste Halesegment (se Tab. XII, 

 Fig. 23 — 27) er noget hengere end de foregaaende, 

 og har oventil paa hver Side afMidtlinien en rund- 

 agtig Knude besat med en Kreds af smaa Tagger, 

 i hvis Midte en fin Sandseliorste sees at rage frem 

 (se Fig. 28). Ved Ihiden a f Segmentet tindes paa 

 den ventrale Side Aiuihiabningen, og unii(hlell)art 

 over denne tVnisætter Segmentet sig i en t\-nd lio- 

 rizontal Plade. der skyder frem bagtil nudlem Basi.s 

 at de 2 Haletraade. 



rounded ])ronunence, upon whieli the 2 eompound 

 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 pai't, there is a distinct 

 keel, which becomes more prominent posteriorly, 

 and ends in a sharp projection at the bottom 

 of the posterior emargination of tlie carapace. As 

 stated above, the carapace is completely coalesced 

 in front witli the head, and there forms, below 

 (see fig. 2), a crescent-shaped horizontal duplicature, 

 whereby the head acqiiires a ^n-onounced shovel- 

 like shape (see also fig. 3). "\\'itli 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 tlie \\lu)le, of a, rather 

 soft consistence. It is, as usual, composed of two 

 lamellæ, one external, very thin, jjerfectly 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 wliieh the blood circulates, and also 2 very 

 higlily developed shell glands. These are partially 

 visible externally in the form of long oval, rather 

 ensiformly curved areas, extending from the cervical 

 sulcus along the sides of the free portion of the 

 carapace (see fig. o) They each consist (see PI. 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 

 (PI. XIII, 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 fii'st 11 belong to the meso- 

 some, and each carry one pair of legs, whereas the 

 following 11 segments, which belong to the nieta- 

 some, each carry several jiairs of legs. The last 

 6 segments have no legs, and therefore represent 

 the tail pro])er. They are very sharply defined, the 

 posterior edge being somewhat raised, and armiMl 

 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 Ihan the ]]rece- 

 ding ones, and has above, on each side of the me- 

 dian line, a round ]>rominence surrounded liy a cinde 

 of snuill denticles, t'roni the midst of which a tine 

 sensory hristle is seen to project (see fig. 28). At 

 the end of the segment, on the ventral side, is tlie 

 anal oi'ificc, and inimciliatcdy above it, the segment 

 is i)rolongcil into a thin horizontal himelhi, urotrn- 



