Among univalves, the most prominent pearl-producer is probably the common conch or great conch (_Strombus gigas_) of the West Indies and the Florida coast, which secretes beautiful pink pearls of considerable value. This is one of the largest of the univalve shells, some individuals measuring twelve inches in length, and weighing five or six pounds. The graceful curves and the delicate tints of lovely pink color make it exceedingly attractive. The conch abounds in the waters of the West Indies, especially in the Bahamas, where many thousands are annually taken for the shell, which forms quite an article of commerce. The flesh is esteemed as food and is also used for bait; and it is particularly in preparing for these purposes that the pearls are found, as no established fisheries exist for the pearls alone. The ear-shells or abalones (Haliotidæ) found on the coasts of California, Japan, New Zealand, and other localities in the Pacific, secrete pearly concretions, sometimes with fine luster, but usually of small value. These shells resemble in general outline the form of the human ear. Distinguishing characteristics are the flatly-spiral bowl-like shape, and the regular series of holes in the back near the distal margin, for the admission of water to the respiratory organs. The holes are on the left side and parallel with the columellar lip, and those nearest the apex close up as the shell increases in size. The shells are rough externally, but beautifully nacreous within. In variety and intensity of coloring, the nacre is superior to that of the pearl-oysters, but it is not so harmonious, and it does not form so thick and flat a layer. Abalone pearls are especially interesting on account of their brilliant and unusual colors. Green predominates, but blue and yellow also occur. Although commonly very small, some of the well formed ones exceed seventy-five grains in weight, and those of irregular shape may be very much larger. The ear-shells also produce many irregular pearly masses. Although these are without an established commercial value, their beautiful greenish or bluish tints adapt them for artistic jeweled objects, such as the body of a fly or of a beetle. Similar concretions are found in species of turbos and turbinella, especially the Indian chank (_Turbinella rapa_), which yields pink and pale red pearls. The pearly nautilus (_Nautilus pompilius_) yields a few yellowish pearls, especially those taken in Australian waters; but from the paper nautilus—“the sea-born sailor of his shell canoe”—no pearls are obtained, owing to the non-lustrous nature of the shell.