værende Form viser mest Afinitet. At den imid- 

 lertid ikke længere kan opfattes som en virkelig 

 rhyllo])ode, derom kan der vel neppe for Tiden være 

 mere end en Mening, efterat dens anatomiske Byg- 

 ning, navnlig ved Prof. Claus's ndmærkede Under- 

 søgelser. er bleven noiere udredet. Sporgsmaalet er 

 nu, om de Eiendommeliglieder, denne Form viser i 

 anatomisk Henseende, gjor det alisolut nedvendigt at 

 skille den helt nd fra de ovrige Entomostraceer som 

 Typen for en egen Orden. Saagodtsom samtlige 

 Forskere synes for Tiden i Virkeligheden at være 

 af denne Mening, og baade Packard's Benævnelse 

 Fhyllocaricla og den af Claus foreslaaede Leptostraca 

 er beregnet paa at udtrykke en distinct Orden. 

 Undersoger vi imidlertid, hvorledes Forholdet er 

 med de for Tiden ialmindelighed til Branchiopodernes 

 Orden henførte Former, saa vil vi ogsaa her stode 

 paa særdeles store og væsentlige Forskjelligheder i 

 den anatomiske Bygning ; ja de saakaldte7?rrt«c/«'Mrer 

 (Argulu.s), som vel de fleste Forskere nu er enige 

 om at henføre til Branchiopodernes Orden, forekom- 

 mer mig endog, saavel hvad den ydre Habitus som 

 den indre Organisation og Levevis angaar. at skille 

 sig endnu betj-delig mere fra de tj-piske Branchio- 

 poder end Tilfældet er med Nehcdin. Hos denne 

 sidste Slægt er der ialfald en Character, og det 

 netop den for Branchiopodernes Orden mest beteg- 

 nende, der staar i den bedste Harmoni med hvad vi 

 finder som typiskt for denne Krebsdja-gruppe ; jeg 

 mener Forkropslemmernes Bygning. Disse viser ikke 

 blot ved sin udpræget bladdannede Form den storste 

 Lighed med samme hos virkelige Branchiopoder; 

 men, hvad der er af end større Vægt, deres respi- 

 ratoriske Function er fuldkommen ligesaa tydeligt 

 udpræget som hos de mest typiske Former blandt 

 hine. Alene denne ene Character synes mig at 

 maatte stemple Slægten XebaJia som en veritabel 

 Branchiopode, og ialfald at være af adskillig større 

 Vægt end Mesteparten af de Characterer, man har 

 anført for at modbevise en saadan Antagelse, og 

 hvoraf flere faktisk er fuldstændig ubrugelige. Efter 

 min Mening bør derfor Slægten Nehalia henføres til 

 Branchiopodernes Orden, om den end her maa danne 

 Typen for en egen, i visse Henseender meget ano- 

 mal Afdeling eller L'nderorden. for hvilken den først 

 af Packard foreslaaede Benævnelse 1'hyUocarida vil 

 kunne bibeholdes. 



I den nyere Tid har man troet i nogle, tildels 

 kjæmpemæssige, fossile Former fra den palæozoiske 

 Formation [Ceratiocaris, Dilhi/rocaris etc.) at gjeu- 

 kjende visse for Slægten Nebalia eiendommelige Cha- 

 racterer, saaledes Legemets almindelige Form. Ud- 

 viklingen af Rygskjoldet og navnlig den meget 

 characteristiske bevægelige Pandeplade* og, skjondt 



stracans, and among these the Branchiopods are 

 tho.'^e with which the present form exhibits most 

 affinity. That it ma}-, however, be no longer regarded 

 as a genuine Phyllopod, there can, now be scarcelj' 

 any diversity of opinion since its anatomical struc- 

 ture has been preciselj' elucidated, especially through 

 Prof. Claus"s admirable investigations. The question 

 now is, whether the peculiarities this form exhibits 

 in anatomical respects makes it absolutely neccessaiy 

 to separate it entireh- from the other Entomostra- 

 cans, as the type of a special order. Nearly all 

 investigators appear, at present, to really entertain 

 that view, and both Packard's appellation, FhjUo- 

 carifla, and that proposed bj- Claus, Leptostraca, are 

 intended to express a distinct order. If we, how- 

 ever, investigate what the relations of the forms at 

 present generalh- assigned to the order of Branchio- 

 pods are, we will also here meet with particularly 

 great and material divergencies in the anatomical 

 structure; indeed the so-called i?/'flH(7;/;(»-a (Argulus), 

 which most investigators are now, we think, unan- 

 imous in assigning to the order of Branchiopods, 

 yet appeal's to me, both in regard to external habi- 

 tus, internal organization, and the mode of life, to 

 distinguish itself even more considerably from the 

 typical Branchiopods than is the case with NehaJia. 

 In the latter genus there is, at any rate, one char- 

 acter, and just the one most characteristic of the 

 order of Branchiopods, which stands in the most 

 perfect harmony with what we find to be tj^pical 

 in that group of Crustaceans. I refer here to the 

 structure of the appendages of the anterior division 

 of the body. These exhibit, not only in their dis- 

 tinguished foliaceous form the greatest similarity 

 with the same limbs in genuine Branchiopods, but, 

 what is of still greater importance, their respira- 

 tory function is perfectl}- as prominent as in the 

 most t3'pical form of Branchiopods. That single 

 characteristic alone, it appears to me, must stamp 

 the genus Xehalia as a true Branchiopod, and, in 

 any case, is of considerabh- more importance than 

 the greater part of the characteristics that have 

 been adduced to 'disprove such an assumption, and 

 some of which are really perfectly unserviceable. 

 In my opinion the genus XeJialia ought, therefore, 

 to be assigned to the order of Branchiopuds, even 

 although it here must form the type of a special, 

 in certain respects verj' anomalous division or sub- 

 order, for which the appellation I'Jii/llocarida, first 

 proposed by Packard, may be retained. 



In later times it has been thought, that we, in 

 some parth^ gigantic fossil forms from the Paleo- 

 zoic formation {Ceratiocaris, DitJn/rocaris &c.) were 

 able to recognize certain characteristics peculiar to 

 the genus Nebalia, for instance the general form 

 of the body, the development of the carapace, and 

 especiall\- the very characteristic mobile frontal 



