10 



son. Overhovedet synes kun denne ene Art at være 

 observeret af andre Forskere. Fra den følgende 

 meget nærstaaende, skjendt sikkert speoifiskt for- 

 skjellige Form er den strax kjendelig ved de vel 

 udviklede og med tydeligt Pigment og Synselementer 

 forsynede Øine, samt ved Pandepladens forskjellige 

 Form. 



Beskrivelse af Hunnen. 



Legemets Længde, regnet fra Spidsen af Pande- 

 pladen til Enden af de sammenlagte Halegrene, er 

 Los de største af mig ohserveredeExemplarer, tagne 

 ved Lofoten, omtrent 1"2 mm. Exemplarer fra vor 

 Syd- og Vestkyst er ialmindelighed noget mindre. 



Legemets Form (se Tab. I, Fig. 1 og 2) maa 

 idetliele siges at være temmelig slank, især naar 

 man observerer Dyret i levende Tilstand. Paa de 

 i Spiritus opbevarede Exemplarer synes ialmindelig- 

 lied Legemet noget kortere og mere undersætsigt 

 paa 'Grnnd af en ved Spiritusens Action frembragt 

 kjendelig Contraction i Ledføiningerne mellem de 

 forskjellige Segmenter; noget der ogsaa bemærkes 

 paa de fleste af andre Forskere givne Figurer af 

 dette Dyr. Hele den forreste Halvpart af Legemet 

 dækkes mere eller mindre fuldstændigt af Rygskjol- 

 det, bag hvilket den bagtil successivt afsmalnende 

 og meget bevæ.gelige Hale rager frit frem. Den 

 habituelle Lighed med en Copepode (navnlig visse 

 Herpacticider) er umiskj endelig og bliver endmere 

 paafaldende, naar man observerer Dyret i levende 

 Tilstand, idet Bevægelserne foregaar paa en fuld- 

 kommen lignende Maade. 



Rygskjoldet er meget stærkt samraentrykt fra 

 Siderne, saa at dets Brede kun lidet overgåar den 

 halve Høide, og, da det desuden mellem sine Side- 

 dele fuldstændig indeslutter ikke blot Munddelene, 

 men ogsaa alle følgende Forkro])slemmer (Pranchial- 

 fødderne), har det mere Lighed med en tveklappet 

 Skal, saaledes som vi linder det hos visse Phyllo- 

 poder og Cladocerer. Ogsaa i andre Henseender er 

 denne Lighed tydeligt fremtrædende. Saaledes vil 

 man finde, at dette Rygskjold kun paa et meget 

 indskrænket Omraade helt fortil og oventil, dan- 

 ner den umiddelbare Kropsvæg (se Tab. IL Fig. 1), 

 medens det forøvrigt kun gan.ske løst dækker Le- 

 gemet, som derfor frit kan bevæges indenfor samme. 

 Endelig kan de 2 Sidedele, eller Val vier, ligesom 

 hos de ovennævnte Branchiopoder, bevæges imod 

 hinanden ved Hjælp af en stærk transversal Ad- 

 ductormuskel (Tab. IL Fig. 7, ms), der lige liag 

 Munddelene forbinder de 2 Valvler med hinanden. 

 Insertionen af denne Adductormuskel er ogsaa ud- 

 vendigt meget tydeligt at se i den forreste Del af 

 hver Valvel, nærmere Dorsalsiden, i Form af en vel 

 begrændset oval Area, hvori bemærkes en Ansam- 



Altogethei-, only this single species appears to have 

 been observed by other investigators. From the 

 following very closely related, although certainly 

 specifically different, form, it is immediately distin- 

 guishable by the -well developed eyes furnished 

 with distinct pigment and visual elements, and also 

 by the different form of the frontal plate. 



Description of the female. 



The length of the body measured from the tip 

 of the frontal plate to the extremity of the folded 

 caudal rami is, in the largest specimens that I 

 have observed, taken off Lofoten, about 12 mm. 

 Specimens from the south and west coasts of Norway 

 are generally somewhat smaller. 



The form of the body (see PI. I fig. 1 and 2) 

 must be said to be, on the whole, rather slender, 

 especially when the animal is obsei'ved in the liv- 

 ing state. In specimens preserved in alcohol, the 

 body appears, in general, to be somewhat shorter 

 and stouter, owing to an appreciable contraction of 

 the articulations between the various segments, pro- 

 duced by the influence of the alcohol, a circumstance 

 also noticed in the illirstrations of this animal sup- 

 plied by most other naturalists. The entire fore- 

 most half of the animal is covered more or less 

 completely by the carapace, behind which the grad- 

 ually backwards-diminishing and very mobile tail 

 projects freely. The habiti^al resemblance to a 

 Copepod (especially certain Harpaeticids) is unmis- 

 takeable and becomes still more conspicuous when 

 we observe the animal in the living state, as the 

 movements occur in an exacth' similar manner. 



The carapace is very strongly compressed from 

 the sides, so that its breadth Imt little exceeds half 

 the height, and, besides, as it completely encloses 

 between its lateral parts not only the oral parts 

 but also all the succeeding appendages of the anterior 

 division of the body (the branchial legs), it has 

 more of resemblance to a bivalve shell, such as we 

 find it in certain Phyllupods and Cladoceres Also 

 in other respects is this resemblance distinctly pro- 

 minent. We may thus observe that this carapace 

 forms, only within a very limited space quite in 

 front and above, the immediate wall of the body 

 (see PI. II fig. 1), whilst it, otherwise, only quite 

 loosely covers the body, which can therefore move 

 itself freely within it. Finally, the 2 lateral parts 

 or valves can, as in the above-mentioned Branchio- 

 pods, be moved towards each other with the aid of 

 a powerful transversal adductor muscle (see PI. 11 

 fig. 7, ms.) which immediately behind the oral parts 

 connects the 2 valves to each other. The insertion 

 of this adductor muscle may also be very distinctly 

 observed from the exterior, in the foremost part 

 of each valve next the dorsal side, in tlie form of 



