M.T. Thorell on the Species of the Argulidee. 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 Argulidz, 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 cf 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- 
tenne breves; primi paris unco incurvo armate, cum maxilli- 
pedibus primi paris ad figendum apte ; secundi paris simplices, 
articulis paucis (4-5). “Os in siphonem productum, mandi- 
bulas et, si que adsunt, maxillas quoque includentem ; maxilli- 
pedes fortissimi, anteriores plerumque cotyledones formantes. 
Truncus segmentis 4, distinctis; pedum paria 4, natatoriorum, 
biramium, appendicibus branchialibus carentium. Cauda non 
segmentata, plana, foliacea, respiration inserviens, testes aut 
receptacula seminis includens. Metamorphosis incompleta. 
Animalia in cute externa, in cavitate branchiali vel in bran- 
chiis piscium (et batrachiorum) parasitantia. 
Fam. AreuLip#, Leach, cet. (Argulina, Kr., Burm., cet.), 
Character subordinis etiam familiz unice. 
Gen. I. Arcuxus, Miiller (1785). 
Monoculus, Linn., cet.; Binoculus, Geoffr., cet.; Ozolus, Latr.; Agenor, 
Risso. 
Maxillipedes primi paris in adultis cotyledones formantes. 
a. Pedes flagello carent. Stimulus ante siphonem adest. 
Sipho mandibulas et maxillas continet. (4genor, Risso.) 
1. A. purpureus (Risso). 
?2. A. giganteus, Lucas. 
(3. Pedes parium 1™ et 2" flagello instructi. Stimulus adest. 
Sipho mandibulas et maxillas continet. (Argulus, Mill.) 
3. A. foliaceus (Linn.). 
4. A. coregoni, Thor. 
5. A. pugettensis, Dana. 
6. A. catostomi, Dana et Herr. 
