Page:Natural History, Mollusca.djvu/223

Rh

Another group of Limpet-like shells are associated under this title, represented poorly in the British seas, but numerous and much varied in their details in those of the tropics. They are commonly more or less circular in outline, rising into a cone, the tip of which sometimes is produced into a spire, which falls over. In the interior of the shell, there is in some of the genera a variously shaped shelly plate, which is quite wanting in others.

The animal has a distinct head furnished with tentacles, and eyes placed at their bases; the muzzle is not produced into a proboscis. The tongue is armed with teeth, arranged in rows of seven each, the central one differing in form from the others. The gill plume is single, and the foot is unfurnished with lateral filaments.

Some of the genera, at least, sit on and hatch their eggs. According to Audouin and Milne Edwards, the parent Calyptræa disposes them under her belly, and preserves them as it were imprisoned, between the foot and the foreign body to which she adheres, her patelloid shell thus serving not only to cover and protect herself, but as a shield to her offspring. These eggs are oval bodies of a yellow colour, enclosed in membranous capsules, which are elliptical, flattened, translucid, and filled with an albuminous matter. The number of these little capsules varies from six to ten; they are connected among themselves by a footstalk, so as to represent a sort of rosette; each of them contains from eight to ten eggs. It appears