M. T. Tliorell on the Systematic Position of the Argulidse. 285 



fining strictly the limits of the Branchiopoda among the other 

 lower Crustaceans — the compound eyes with unfacetted cornea, 

 the absence of palpi or branchial appendages on the oral organs, 

 lobed or cloven respiratory or swimming-feet without median 

 plates, distinct sexes — occur in the Argulidse. The discrepancies 

 which depend on their parasitic habits cannot be put forward as 

 reasons for the isolated position of the Argulidse, at least as long 

 as parasitic and free Copepoda are unanimously referred to the 

 same order. If we look at these differences, we find that be- 

 tween the Argulidse on the one side, and the Phyllopoda and 

 Cladocera on the other, no greater dissimilarities exist than 

 those which separate these two groups from each other. Al- 

 though indeed it must be admitted that the Argulidse stand 

 nearer to the Phyllopoda than to the Cladocera, it seems to us 

 nevertheless that the differences we have mentioned (we would 

 recall in particular the form and function of the tail, and the 

 presence of receptacula seminis), in conjunction with the cha- 

 racters which are correlative to their parasitic nature, are suf- 

 ficiently sti'ong to set aside the notion of the introduction of 

 the Argulidse among the Phyllopoda. We regard them con- 

 sequently as a group of the same systematic value as these and 

 the Cladocera — that is to say, a suborder, on a par with these, in 

 the order of the Branchiopoda, — and propose, since Argulida or 

 Argulina are only suitable as family names, for this suborder the 

 appellation Branchiura, drawn from the characteristic condition 

 of the tail in these animals. Just as the Cladocera are composd 

 of one family only (the Daphnidse), the Branchiura for the pre- 

 sent comprise only one family (the Argulidse). 



We think that the Branchiopoda (if we reserve the fossil 

 Trilobites, which undoubtedly belong to them, and with whose 

 oral organs and feet we are not sufficiently acquainted) may be 

 characterized as follows : — 



BRANCHIOPODA. 



Oris partes palpis fere semper carentes, appendicibus branchialibus 

 nuUis ; maxillarum par 1-0, maxillipedum 2-0. Oculi duo magni 

 laterales, saepe in unum coaliti, e multis bacillis crystallinis compo- 

 siti, cornea supra sequali prsediti. Segmentorum et pedum numerus 

 valde varians : pedes fissi vel foliacei, appendicibus branchialibus 

 plerumque instruct], nulla lamina intermedia bini conjuncti. Corpus 

 testa membranacea, plerumque bivalvi, ssepissime inclusum. Sexus 

 distincti. 



I. PHYLLOPODA. 



Oculi compositi plus minus sejuncti. Pedum paria 10-60. Meta- 

 morphosis completa. Libere natantia. 



1. Branchipodid^. 2. Afodid^. 3. Limnadidjs. 4. Ne- 



BALIDiE. 



