CIRRIPEDIA.
(Barnacles, Acorn-Shells.) Char.—Body chitinous or chitino-testaceous, subarticulated, mostly symmetrical, with aborted antennae and eyes ; thorax attached to the sternal surface of the carapace, with six pairs of multiarticulate, biramous, setigerous limbs ; metamorphosis resulting in a permanent para sitic attachment of the fully-developed female to some foreign body.
The fossil Cirripedes belong chiefly to the sessile division, and consist of the ordinary forms of the still-existing Balanidce. They are rare in the eocene tertiary, but more abundant after wards. The Balanus porcatus attains a great size in the Shelly beds of northern drift ; its large basal plate, when detached, is a puzzling fossil, and has caused some mistakes. A Coro nula has been found in the middle division of the crag which has afforded so many cetaceous bones. Remains of peduncu lated Cirripedes occur in older deposits, but are mostly scarce and fragmentary. A species of Pollicipes is found adhering to drift-wood, perforated by bivalves, in the Has ; another occurs in the Oxford clay, attached in groups to drift-wood, and the shells of Ammonites, which probably floated in the sea after death. The chalk affords many species of Pollicipes and Swi
pe/inn, a species of the anomalous genus Verruca, and the only extinct genus of Cirripedes—Loricula (fig. 10, 6). This remarkable fossil is found attached to Ammonites, and exhi bits only one side in any of the examples hitherto found. In this unsymmetrical development and the imbrication of its valves it more resembles Verruca than any other Cirriped. " During the deposition of the great cretaceous system, the Lepacliche arrived at their culminant point : there were then three genera, and at least thirty-two species ;" whereas at the present day the Philippine Archipelago, which is the richest marine province, affords but five species.