M. T. Thorell on the SjJccies of the Argulidse. 437 



The arrangement which I have adopted can therefore be only 

 provisional^ and is put forward merely with a view to draw 

 attention, on the part of those who have opportunities for 

 examining new or incompletely known Argulidse, to the cha- 

 racters which have seemed to me the most important for the 

 systematic arrangement of these animals. Excepting in the 

 case of the three European species, which I have had occa- 

 sion to examine myself, the diagnoses are compiled from the 

 descriptions and figures of others. I shall first range the fifteen 

 (or sixteen) known Argulids in the order which seems to me the 

 most natural, and then briefly particularize each species sepa- 

 rately. 



BRANCHIURA. 



Corpus depressum, capite in scutum magnum, postice ple- 

 rumque bifidum dilatato; oculi compositi longe sejuncti. An- 

 tennae breves; primi paris unco incurvo armatse, cum maxilli- 

 pedibus primi paris ad figcndum aptse ; secundi paris simplices, 

 articulis paucis (4-5). Os in siplionem productum, mandi- 

 bulas et, si quse adsunt, maxillas quoque ineludentem ; maxilli- 

 pedes fortissimi, anteriores plerumque cotyledones formantes. 

 Truncus segmentis 4, distinctis ; pedum paria 4, natatoriorum, 

 biramium, appendicibus branchialibus carentium. Cauda non 

 segmentata, plana, foliacea, respirationi inserviens, testes aut 

 receptacula seminis includcns. Metamorphosis incompleta. 



Animalia in cute externa, iu cavitate branchiali vel in bran- 

 chiis piscium (et batrachiorum) parasitantia. 



Fam. ARGULiDiE, Leach, cct. {Argulina, Kr., Burm., cet.). 

 Character subordinis etiam familise unicse. 



Gen. I. Argulus, Miiller (1785). 



Monoculus, Linn., cet. ; Binoculus, GeofFr., cet. ; Ozolus, Latr. j Agenor, 

 Risso. 



MaxilHpedes primi paris in adultis cotyledones formantes. 



a. Pedes flagello carent. Stimulus ante siphonem adest. 

 Sipho mandibulas et maxillas continet. {Jgenor, Eisso.) 



1. A. purpureus (Risso). 

 ? 3. A. giganteus, Lucas. 



/3. Pedes parium r°' et 2'" flagello instruct!. Stimulus adest. 

 Sipho mandibulas et maxillas continet. {Argulus, Miill.) 



3. A. foliaceus (Linn.). 



4. A. coregoni, Thor. 

 ?5. A. pugettensis, Dana. 



6. A, caiostomif Dana et Herr. 



