CHAP. XXII.] 
MOLLUSC A 
509 
Family 8.— PYRAMIDELLID,®. (10 Genera, 220 Species.) 
Distribution.— These turreted shells are very widely distri- 
buted both in temperate and tropical seas; and most of the 
genera have also a wide range. There are about 400 extinct 
species, from so far back as the Lower Silurian to the Pliocene 
formations. 
Family 9. — CERITHIADiE. (5 Genera, 190 Species.) 
Distribution. — These are marine, estuary, or fresh-water 
shells, of an elongated spiral form ; they have a world- wide 
distribution, but are most abundant in the Tropics. Potamides 
(41 sp.), is the only fresh-water genus, and is found in the 
rivers of Africa, India and China, to North Australia and Cali- 
fornia. Another genus is exclusively fossil, and there are 
about 800 extinct species, ranging from the Trias to the Eocene 
and recent formations. 
Family 10. — MELANIADiE. (3 Genera, 410 Species.) 
Distribution. — Fresh-water only : lakes and rivers in warm 
countries, widely scattered. South Palsearctic and Australian 
regions, from Spain to New Zealand ; South Africa, West Africa, 
and Madagascar; United States. There are about 50 -fossil 
species, from the Wealden and Eocene to recent formations. 
Family 11. — TURRITELLIDiE (5 Genera, 230 Species.) 
Distribution. — Universal. Caecum is found in north tem- 
perate seas only. The other genera are mostly tropical, but some 
species reach Iceland and Greenland. There are near 300 
species fossil, ranging from the Neocomian to the Pliocene 
formations. 
