There are three varieties, spiral, univalve, and bivalve.
"Missionary Travels and Researches in South Africa" by David Livingstone
Group of Upper Silurian Univalves.
"The Ancient Life History of the Earth" by Henry Alleyne Nicholson
The objects are generally made from large pear-shaped sections of the lower whorl of marine univalves.
"Illustrated Catalogue of a Portion of the Collections Made" by William H. Holmes
Cochleate: spirally twisted like a screw or a univalve shell.
"Explanation of Terms Used in Entomology" by John. B. Smith
The mother-of-pearl which lines some shells, both univalve and bivalve.
"The Sailor's Word-Book" by William Henry Smyth
The Japanese tops are of several kinds, some are made of univalve shells, filled with wax.
"Child-Life in Japan and Japanese Child Stories" by Mrs. M. Chaplin Ayrton
Caracol, a conch, a univalve shell.
"The Arawack Language of Guiana in its Linguistic and Ethnological Relations" by Daniel G. Brinton
The eggs of the univalve Mollusca are hardly less varied in the shapes they take.
"Encyclopaedia Britannica, 11th Edition, Volume 9, Slice 1" by Various
But a great number of the bivalve Testacea, and many also of the turbinated univalves, burrow in sand or mud.
"Principles of Geology" by Charles Lyell
On the other hand, Volutes and other genera of univalve shells, usually met with only in tertiary strata, occur.
"A Manual of Elementary Geology" by Charles Lyell