værende Form viser mest Afinitet. At den imid- 

 lertid ikke længere kan opfattes som en virkelig 

 Phyllopode, derom kan der vel neppe for Tiden være 

 mere end en Mening, efterat dens anatomiske Bj-g- 

 ning. navnlig ved Prof. Claus's udmærkede Under- 

 søgelser, er bleven noiere udredet. Sporgsmaalet er 

 nu, om de Eiendommeligheder, denne Form viser i 

 anatomisk Henseende, gjor det absolnt nødvendigt at 

 skille den helt ixd fra de øvrige Entomostraceer som 

 Typen for en egen Orden. Saagodtsom samtlige 

 Forskere sj^nes for Tiden i Virkeligheden at være 

 af denne Mening, og baade Packard's Benævnelse 

 Fhyllocariåa og den af Clans 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 saakaldte Brawc/irører 

 (Argulns), 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 betydelig mere fra de tj'piske Branchio- 

 poder end Tilfældet er med Nehalia. 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 Krebsdyrgruppe ; jeg 

 mener Forkropslemmernes Bygning. Disse viser ikke 

 blot ved sin udpræget bladdannede Form den største 

 Lighed med samme hos virkelige Branchiopoder; 

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

 ratoriske Fvinction er fuldkomnien ligesaa tydeligt 

 vidpræget som hos de mest typiske Former blandt 

 hine. Alene denne ene Character synes mig at 

 maatte stemple Slægten Nehalia 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 Underorden, for hvilken den først 

 af Packard foreslaaede Benævnelse Phi/Uocarida vil 

 kunne bibeholdes. 



I den nyere Tid har man troet i nogle, tildels 

 kjæmpemæssige, fossile Former fra den palæozoiske 

 Formation (Ceratiocaris, Bithyrocaris etc.) at gjen- 

 kjende visse for Slægten Nehalia eiendommelige Cha- 

 racterer, saaledes Legemets almindelige Form, Ud- 

 viklingen af Rj'gskjoldet og navnlig den meget 

 characteristiske bevægelige Pandeplade; og, skjøndt 



stracans, and among these the Branchiopods are 

 those with which the present form exhibits most 

 affinity. That it may, however, be no longer regarded 

 as a genuine Phyllopod, there can, now be scarcely 

 any diversity of opinion since its anatomical struc- 

 ture has been precisely elucidated, especially through 

 Prof Claus's admirable investigations. The question 

 now is, whether the peciiliarities this form exhibits 

 in anatomical respects makes it absolutely neccessary 

 to separate it entirely 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, Phi/llo- 

 carida, and that proposed by Claus, Leptostraca, are 

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

 ever, investigate what the relations of the forms at 

 present generally 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?raM(7»'Mra (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 Nehalia. 

 Li 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 gi'eatest similarity 

 with the same limbs in genuine Branchiopods, but, 

 what is of still greater importance, their respira- 

 tory function is perfectly as prominent as in the 

 most typical form of Branchiopods. That single 

 characteristic alone, it appears to me, must stamp 

 the genus Nehalia as a true Branchiopod, and, in 

 any case, is of considerably more importance than 

 the greater paii 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 Nehalia ought, therefore, 

 to be assigned to the order of Branchiopods, even 

 although it here must form the type of a special, 

 in certain respects very anomalous division or sub- 

 order, for which the appellation Phi/Uocarida, first 

 proposed by Packard, may be retained. 



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

 some partly gigantic fossil forms from the Paleo- 

 zoic formation {Ceratiocaris, Dithyrocaris &c.) were 

 able to recognize certain characteristics peculiar to 

 the genus Nehcdia, for instance the general form 

 of the body, the development of the carapace, and 

 especiallj' the ver}' characteristic mobile frontal 



