The pasto duro is largely composed of the genera Stipa and Melica.
The same deposits have also yielded remains of extinct types of kangaroo, some of gigantic size, constituting the genera Sthenurus, Procoptodon and Palorchestes.
Filhol, the fossils themselves represent two genera, Peratherium, containing the greater part of the species, about twenty in number, and Amphiperatherium, with three species only.
Here may be noticed three genera of large extinct marsupials from the Pleistocene of Australia whose affinities appear to ally them to the wombat-group on the one hand and to the phalangers on the other.
The Australian seas are inhabited by many fishes of the same genera as exist in the southern parts of Asia and Africa.
There are genera so far removed from every living genus that many connecting links must have become extinct.
Garrod in 1876 and 1877 who finally divested the Family of these aliens, but until examples of some of the other genera have been anatomically examined it may not be safe to say that they all belong to the Pteroptochidae.
The parasitic Nematodes include by far the greatest number of the known genera; they are found in nearly all the orders of the animal kingdom, but more especially among the Vertebrata, and of these the Mammalia are infested by a greater variety than any of the other groups.
There are many genera and species of leeches, the exact definitions of which are still in need of a more complete survey.
Fresh-water forms, however, are also known, very few as regards species or genera, but often extremely abundant as individuals.
In the British fresh-water fauna only two genera, Hydra and Cordylophora, are found; in America occurs an additional genus, Microhydra.
In all the abovementioned genera, with the exception of Hydra, the life-cycle is so imperfectly known that their true position cannot be determined in the present state of our knowledge.
The characteristic sense-organs are ectodermal otocysts, absent, however, in some genera, in which case cordyli may replace them.
Other genera are Aglauropsis, Gossea and Gonionemus; the last named bears adhesive suckers on the tentacles.
Of doubtful position, but commonly referred to the Trachylinae, are the two genera of fresh-water medusae, Limnocodium and Limnocnida.
In some Indian and Malay Engystomatids of the genera Callula and Microhyla, the tadpoles are remarkably transparent, and differ markedly in the structure of the buccal apparatus.