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Sea Shells of New Zealand

Suture. The line of union between one whorl and the adjacent one in a spiral univalve.

Umbilicus.—A cavity, circular depression or chink at the base of spiral univalves, affording lightness and strength; not present in all. Those possessing it are termed perforate; those without, imperforate.

Umbo (plural, umbones).—The boss or rounded eminence of a circular shield. In bivalves, the umbo is the rounded and elevated portion adjoining the beaks.

Varix (plural, varices).—A large rib, such as those on the Septa costata and the Murex Angasi var. Eos, descending down the whorls. They are usually few in number, and are so named in contradistinction to the ordinary longitudinal ribs on spiral univalves, which are numerous and of much smaller size.

Whorl.—One complete turn of a spiral univalve; the lowest of all, with the aperture—i.e., the body whorl—containing the body of the animal. This is at the anterior end of the shell, as the animal, during its progress, advances this portion of its shell in front. In describing the dimensions of a univalve, the word length denotes the distance between the tip of the spire and the extreme base; the word height signifies precisely the same dimension, but presumably in the empty shell, held in the hand with the spire naturally pointing upwards. In the bivalve the height is invariably the distance measured from the hinge to the opposite point of the ventral margin, the length being always the distance between the anterior and posterior borders. The length is not always the longest diameter: for instance, the Lima bullata is only half as long as it is high.