The Chelydidæ, or fresh-water tortoises with imperfectly retractile heads, have a remarkable distribution in the three great southern continents of Africa, Australia, and South America; the largest number of species being found in the latter country. The genera are:—
Peltocephalus (1 sp.), Podocnemis (6 sp.), Hydromedusa (4 sp.), Chelys (1 sp.), and Platemys (16 sp.), inhabiting South America from the Orinooko to the La Plata, the latter genus occurring also in Australia and New Guinea; Chelodina (5 sp.), Chelemys (1 sp.), and Elseya (2 sp.) from Australia; while Sternotheres (6 sp.), and Pelomedusa (3 sp.), inhabit Tropical and South Africa and Madagascar.
Family 59.—TRIONYCHIDÆ. (3 Genera, 25 Species.)
| General Distribution. | |||||
 | |||||
| Neotropical Sub-regions. | Nearctic Sub-regions. | Palæarctic Sub-regions. | Ethiopian Sub-regions. | Oriental Sub-regions. | Australian Sub-regions. |
| — — — — | — — 3 — | — — — 4 | 1. 2. 3 — | 1. 2. 3. 4 | — — — — |
The distribution of the Trionychidæ, or Soft Tortoises, is very different from that of the Chelydidæ, yet is equally interesting. They abound most in the Oriental region, extending beyond it to Northern China and Japan. In the Nearctic region they are only found in the Eastern States, corresponding curiously to the distribution of plants, in which the affinity of Japan to the Eastern States is greater than to California. The Trionychidæ are also found over the Ethiopian region, but not in Madagascar.
The genera are,—Trionyx (17 sp.), which extends over the whole area of the family as above indicated; Cycloderma (5 sp.), peculiar to Africa; Emyda (3 sp.), the peninsula of India, Ceylon, and Africa.
Family 60.—CHELONIIDÆ. (2 Genera, 5 Species.)
General Distribution.—All the warm and tropical Seas.
The Marine Turtles are almost universally distributed. Dermatochelys (1 sp.), is found in the temperate seas of both the Northern and Southern Hemispheres; Chelone (4 sp.), ranges over all the tropical seas—C. viridis, the epicureans' species, inhabiting the Atlantic, while C. imbricata which produces the "tortoiseshell" of commerce is found in the Indian and Pacific oceans.
Remarks on the Distribution of the Chelonia.