121 



Halen (Fig. 7, 8) er meget liden og rudimentær, 

 ikke omboiet, og kan heller ikke i Regelen strækkes 

 .synderlig langt ud fra Skallen. Den ender i 2 skraat 

 nedadrettede og jevnside.s liggende Flige af triangu- 

 lær Form og tæt cilierede i Kanterne, liver bærende 

 i Spidsen en liden, som det sjnies, fuldstændig ube- 

 vægelig Torn, der aabenbart svarer til Haleklorne 

 hos andre bivalve Phyllopoder. Dorsalt findes om- 

 trent paa Midten af Halen et stumpt Fremspring, 

 hvortil de 2 Haleborster er fæstede. Disse er vel i 

 udviklede, tydeligt 21eddede og tæt cilierede. Ha- 

 lens ventrale Side er delvis dækket af en eiendom- 

 melig, operkelformig Plade (op), der udgaar fra dens 

 Basis, og hvortil intet tilsvarende kjendes hos andre 

 Phyllopoder. 



De sammensatte Øine (Fig. 11, o) er beliggende 

 nær Foi^kanten af Hovedet, omtrent ved Enden ai 

 den Iste Trediedel af dets Længde. De er forholds- 

 vis smaa og stoder umiddelbart sammen i Midten, 

 saa at de egentlig tilsammen danner et enkelt j 

 Organ, paa hvilket dog de 2 oprindelige Halvdele 

 let lader sig paavise, naar Organet sees forfra (Tab. 

 XVin, Fig. 4) eller nedenfra (Tab. XIX, Fig. 13, o). 

 De er omgivne af en fælles Kapsel og viser et stort 

 Antal af smaa Krystalkegler udstraalende til alle 

 Sider fra det morke Pigment. Som hos Linmadia, 

 er de til en vis Grad bevægelige ved Hjælp af 3 fra 

 Hovedets Integument til hver Halvdel udgaaende 

 Muskler (se Fig. 11). 



I ganske kort Afstand nedenfor de sammensatte 

 Øine ligger det enkle Øie (Fig. 11, 13, 14, or. Fig. 15). 

 Det er af en noget uregelmæssig afrundet eller ret- 

 tere kubisk Form og \'iser ved nøiere Undersøgelse, 

 ligesom hos Linmadia, 4 Flader indrammede af et 

 morkt Pigment. Fladerne er temmelig stærkt ud- 

 buede og viser under visse Belysninger en lignende 

 iriserende Glands som hos hin Slægt. Det er holdt 

 i Situs ved fine til Hovedets Integument gaaende 

 Ligamenter, hvoraf et fæster sig til Forkanten af 

 Hovedet ved Basis af Rostrum (Fig. 11, p). 



Umiddelbart foran det enkle Øie bemærkes i 

 Hovedets Integument 2 jevnsides stillede aflangt 

 ovale Felter (Fig. 11, ol), der er meget skarpt con- 

 turerede og har til Underlag en blod Masse af til- 

 syneladende ganglios Natur. Ethvert af disse Feld- 

 ter (se Fig. 12) er dækket af en meget delicat Mem- 

 bran, hvorfi-a et Antal af fine Haar eller Cilier 

 springer frem, hvert udgaaende fi'a en liden knop- 

 formig Fortykkelse i Membranen. Der kan neppe 

 være nogen Tvivl om, at disse eiendommelige Dan- 

 nelser, der ogsaa er omtalte af Grube, repræsenterer 

 et Slags Sandseredskaber, men af hvilken Art er 

 vanskeligt at sige. Endnu en eiendommelig Dan- 

 nelse maa her omtales. Folger man Dorsalkanten 



The tail (figs. 7 and 8) is very small and rudi- 

 mentary, is not bent down, and cannot as a rule be 

 extended very far from the shell. It ends in 2 obli- 

 quely-pointing, juxtaposed lobes of a triangular 

 shape, and thickly ciliated at the edges, each car- 

 rying at the point a small, apparently quite immov- 

 able spine, which evidently answers to the oaiidal 

 claws in other bi-valved Phyllopoda. At about the 

 middle of the tail dorsally there is a blunt projec- 

 tion, to which the 2 caudal setæ are attached. The 

 latter are well-developed, distinctly 2-jointed and 

 thickly ciliated. The ventral surface of the tail is 

 partly covered by a peculiar opercular lamella (op), 

 issuing from its base, and to which there is nothing 

 corresponding in other Phyllopoda. 



The compound eyes (fig. 11, o) are situated near 

 the front margin of the head, at about the end of 

 the first third of its length. They are compara- 

 tively small, and meet in the middle, thus forming 

 in reality a single organ, in which, however, the 

 2 original halves may be easily distinguished, when 

 the organ is seen from the front (PI. XVIII, fig. 4) 

 or from below (PI. XIX, fig. 13, o). They are sur- 

 rounded by a common capsule, and exhibit a large 

 number of small crystalline cones radiating to all 

 sides from the dark pigment. As in Limnadm, they 

 are movable to a certain extent by the help of 3 

 muscles issuing from the integument of the head to 

 each half (see fig 11). 



At a very short distance below the compound 

 eyes, is the ocellus (figs. 11, 13, 14 oc, fig. 15). It 

 is of a somewhat irregular, rounded or rather cubi- 

 cal shape, and presents, on a closer examination, 

 just as in Linmadia, 4 surfaces encircled by a dark 

 pigment. The surfaces are not a little convex, and 

 in certain lights, like the above-mentioned genus, 

 have an iridescent lustre. It is held in position by 

 fine ligaments running to the integument of the 

 head, one of which is fastened to the anterior 

 margin of the head at the base of the rostrum (fig. 

 11, p). 



Immediately in front of the ocellus, may 

 be observed, in the integument of the head, 2 

 juxtaposed oblong oval fields (fig. 11. oJ) very 

 sharply outlined, and with a soft mass of an ap- 

 parently ganglionic nature as substratum. Each 

 of these fields (see fig. 12) is covered by a very 

 delicate membrane, from which spring a number 

 of fine hairs or cilia, each issuing from a little 

 nodiform thickening of the membrane. There 

 can hardly be any doubt that these peculiar for- 

 mations, which are also mentioned by Grube, re- 

 present a kind of sensory apparatus, but of what 

 kind, it is difficult to say. Yet another peculiar 

 formation must be mentioned here. In following 



16 • 



G. 0. Sars Fauna Norvegix. 



