Family 16.—HALIOTIDÆ. (6 Genera, 106 Species).
Distribution.—The Ear-shells are most abundant in the Indian and Pacific Oceans; some are found on the east coasts of the Atlantic, but there are very few in the West Indies. Ianthina (10 sp.) consists of floating oceanic snails found in the warm parts of the Atlantic. Three other genera are fossil, and there are near 500 fossil species of this family ranging from the Lower Silurian to the Pliocene formations.
Family 17.—FISSURELLIDÆ. (5 Genera, 200 Species).
Distribution.—All seas. Puncturella (6 sp.) is confined to Northern and Antarctic seas; Rimula to the Philippines; and Parmophorus (15 sp.) from the Cape of Good Hope to the Philippines and New Zealand. There are about 80 fossil species, ranging from the Carboniferous formation to the deposits of the Glacial epoch.
Family 18.—CALYPTRÆIDÆ. (4 Genera, 125 Species).
Distribution.—The Calptræidæ, or Bonnet-Limpets, are found on the coasts of all seas from Norway to Chili and Australia; but are most abundant within the Tropics. The genera are all widely scattered. There are 75 fossil species, ranging from the Devonian to recent formations.
Family 19.—PATELLIDÆ. (4 Genera, 254 Species).
Distribution.—The Patellidæ, or Limpets, are universally distributed, and are as abundant in the temperate as in tropical seas. There are about 100 fossil species, ranging from the Silurian to the Tertiary formations.
Family 20.—DENTALIADÆ. (1 Genus, 50 Species).
Distribution.—The genus Dentalium is found in the North Atlantic, Mediterranean, West Indies and India. There are 125 fossil species, found in various formations as far back as the Devonian in Europe and in Chili.