The _Cryptolepas_ is a new genus of Coronulidæ which inhabits the 58 coast of California, on the singular mysticete recently distinguished by the name of _Rhachianectes glaucus_. The _Platylepas bisexlobata_ has lately been observed on one of the Sirenia, the _Manatus latirostris_. The marine turtles are also invaded by these singular animals, and their peculiar form, joined to their habitat, has given them the name of _Chelonobia_. It is not uncommon to find by the side of these Chelonobiæ, and even upon them, the Tanaïs, Serpulæ, and Bryozoariæ, forming together an animal forest on the cuirass of the turtle. The _Matamata_, a turtle living in the brackish water of Guiana, is covered with a cirrhipede more allied to the ordinary balani than to the chelonobiæ. Other living reptiles are not more exempt from cirrhipedes than turtles; the _Dichelaspis pellucida_ and the _Conchoderma Hunteri_ invade different sea-snakes. Many sharks harbour particular kinds, among which we mention the _Alepas_ of the _Spinax niger_ from the coasts of Norway. The same Alepas has been found on the _Squalus glacialis_ at the same time as the _Anelasma squalicola_. Half a dozen varieties of these are known, one of which inhabits an echinoderm, another a decapod crustacean. These kinds of alepas are so reduced when they are adult, and are so completely despoiled of their distinctive attributes, that it is necessary to study them with especial care in their first dress, in order to recognize their parentage. Other cirrhipedes establish themselves on neighbours of their own class, and we also find crustaceans upon other crustaceans. A pretty genus lives near Cape Verd on the carapace of a large lobster, and spreads itself on the centre of the back like a bouquet of flowers. My son has procured some very fine specimens, an account of which he 59 will publish, together with the other materials which he has collected during his passage across the Atlantic. Mr. John Denis Macdonald found in abundance on the branchiæ of a crab in Australia, the _Neptunus pelagicus_, which he places between the Lepas and the Dichelaspis.