446 M. T. Thorell on the Species of the Argulidse. 



is its proper habitat, since three-fourths of the species which be- 

 long to the genus Argulus, together with all the species of the 

 genus Gyropeltis, are limited thereto. The greater number be- 

 long to the warm parts of that continent : only one species {A. 

 pugettensis) is known from the west coast of (North) America. 

 Of the four non- American species enumerated in our list, Europe 

 has afforded three, and Africa one species (inhabiting the Medi- 

 terranean). 



It is further of importance to note the relative numbers of the 

 species which live in fresh and in salt water. We perceive 

 at once that, as in the other Branchiopoda, the number of 

 freshwater forms preponderates. If we except the four species 

 {A. pugettensis, funduli, and elongatus, with Gyropeltis Kollari) 

 concerning which information in this respect is wanting, it will 

 be seen that of the remaining species only two [A. purpureus 

 and giganteus) are found on fishes which live exclusively in the 

 sea ; all the others are procured from fresh water. It would be 

 of great importance to learn whether or not some of these fresh- 

 water forms can also live in salt water, and, in particular, whether 

 the specie^ {A. coregoni and alos(2, for instance) which live on 

 fishes which undertake journeys from the sea up the rivers 

 follow their hosts when these betake themselves again to the 

 sea. We have already stated that A. catostomi lives also in the 

 brackish water near the mouths of rivers. 



In close connexion with the consideration that the larger 

 number of the Argulidse belong i-i lakes and rivers, and only a 

 small portion to the sea, is the result which we obtain from an 

 inquiry how they are distributed amongst the various groups of 

 fishes. That the Argulids are not always (perhaps never) 

 confined to a single sort of fish is shown in the case of the 

 three European species, which live on fishes of different genera, 

 even of widely separated families — especially A. foliaceus, the only 

 Argulid of whose habitat and mode of life we have a tolerably 

 satisfactory knowledge. This species not only attaches itself 

 to freshwater fish of wholly different orders (Acanthopteri, 

 Pharyngognathi, and Physostomi), but even attacks the larvae 

 of frogs, which is not known to be the case with any of the 

 other species. We are ignorant as to the animals on which 

 three of these {A. pugettensis, A. elongatus, and G. Kollari) 

 occur. The rest have all been found on fishes, and, with 

 the exception of a single species, on Teleostei or bony fishes. 

 Of the other subclasses only one (viz. the Selachia) has figured 

 m our list. A. giganteus is found upon a Rag. Amongst bony 

 fishes it is, as we might almost conclude a priori, especially the 

 order Physostomi which is affected by these parasites. A spe- 

 cies of the Siluroid family harbours G.doradis; many Cyprinoids 



