Distribution.—Lias to Chalk in Europe, India and North America.
Order II.—TETRABRANCHIATA.
Family 7.—NAUTILIDÆ. (1 Genus, 3 Species, Living; 4 Genera, 300 Species, Fossil).
Distribution.—Indian and Pacific Oceans; and the fossil species from the Silurian Period to the Tertiary, in all parts of the world.
Family 8.—ORTHOCERATIDÆ. Fossil. (8 Genera, 400 Species).
Distribution.—Lower Silurian to Lias.
Family 9.—AMMONITIDÆ. Fossil. (14 Genera, 1100 Species).
Distribution.—Upper Silurian to Chalk. Found at 16,000 feet elevation in the Himalayas.
Class.—GASTEROPODA.
Order I.—PROSOBRANCHIATA.