priate to aquatic creatures should once more revisit their thirsty and solidified home.
Of the three orders—Branchiopoda, Ostracoda, and Copepoda—into which the Entomostraca are commonly divided, the present paper touches only the first, and that in two of its divisions—the "leaf-limbed" Phyllopoda, and Cladocera, with conspicuously "branched antennæ." The former especially excite surprise, when they are successfully grown from dried mud, because of their superior magnitude. Some of them also are remarkable for having no carapace, others for being almost entirely enclosed in what looks like the shell of a bivalved mollusc. The Cladocera are closely related to the Phyllopoda, and are most widely known through the little Water-Flea (Daphnia pulex), which, though little, is much larger than the Chydorus sphæricus, to be presently mentioned. The labours of G.O. Sars in Norway, of W. Lilljeborg in Sweden, of Jules Richard in France, of G.S. Brady, D.J. Scourfield, and Thomas Scott in Great Britain, and, in truth, of quite a multitude of learned writers all over the world, have discussed almost every conceivable detail in the structure, habits, and distribution of these animals. Even as to their classification, a very near approach to agreement has been arrived at. All the more desirable is it that every source of confusion should, if possible, be eliminated from the names in common use. But in regard to the genus and family which form the subject of this paper, there is something a little parallel to "the strange case of Dr. Jekyll and Mr. Hyde." It is the object of the following discussion to unmask them, in the sense of showing what are the animals to which the designations that form the title of this paper should rightfully be applied.
It is said of mud that, if you throw plenty, some of it is sure to stick. With scientific names there is an understanding that, if they are thrown according to the rules of the game, they ought to stick at least to some of the objects at which they have been thrown. In early attempts at classification a generic name is often attached to an incoherent miscellany of species. When these are subsequently assorted under appropriate headings, the original generic titles do not always quite know where they are. They stand a chance of being left out in the cold, as things no longer wanted—a kind of disinherited vagrants, blissfully for-
