ABSTRACT
Balanus improvisus extends from Europe to Nova Scotia, thence southward to Patagonia, and up the western coast of South America, some way north of the Equator. Most of the species have considerable ranges; thus of the six species found on the eastern shores of northern America, five of them occur in Great Britain. Balanus improvisus and eburneus are able to survive in brackish water. The different species are attached to various surfaces rocks, shells, timber, floating objects, seaweed, lamelliform corals, Milleporae, Gorgoniae, and even to sponges. The shape of the shell in the different species varies from depressed conical to cylindrical; the latter form being generally assumed when specimens are crowded together; but some species, as balanoides, crenatus, and laevis, seem more subject than others to be thus affected. In typical species the basis is calcareous, and consists of an upper and lower lamina, separated by radiating septa, forming pores.
