_Trionyx muticus_ 531 _Trionyx muticus muticus_ 534 _Trionyx muticus calvatus_ 539 NATURAL HISTORY 541 Habitat 541 Daily and Seasonal Activity 547 Diurnal Habits 547 Behavior Adaptations 549 Movement 552 Nocturnal Habits 553 Seasonal Occurrence 553 Food Habits 555 Reproduction 558 Size of Males at Sexual Maturity 558 Size of Females at Sexual Maturity 560 Sexual Activity 563 Deposition of Eggs 565 Reproductive Potential 568 Eggs 572 Incubation and Hatching 573 Age and Growth 574 Mortality 576 Parasites 576 Economic Importance 577 EVOLUTIONARY HISTORY 578 Distribution 578 Relationships 579 Fossils 582 Phylogeny 585 The Importance of the Study of Turtle Populations in Relation to the History of River Systems 588 SUMMARY 590 LITERATURE CITED 594 INTRODUCTION