CLASSIFICATION 512 Family Geomyidae 512 Subfamily *Entoptychinae 513 Genus *_Pleurolicus_ 514 Genus *_Gregorymys_ 514 Genus *_Grangerimus_ 514 Genus *_Entoptychus_ 514 Subfamily Geomyinae 514 Tribe *Dikkomyini 515 Genus *_Dikkomys_ 516 Genus *_Pliosaccomys_ 517 Tribe Thomomyini 518 Genus _Thomomys_ 518 Subgenus *_Pleisothomomys_ 519 Subgenus _Thomomys_ 520 Tribe Geomyini 521 Genus *_Pliogeomys_ 522 Genus _Zygogeomys_ 523 Genus _Geomys_ 525 Genus _Orthogeomys_ 528 Subgenus _Orthogeomys_ 529 Subgenus _Heterogeomys_ 530 Subgenus _Macrogeomys_ 531 Genus Pappogeomys 532 Subgenus _Pappogeomys_ 534 Subgenus _Cratogeomys_ 535 PHYLOGENY OF THE GEOMYIDAE 536 Primitive Morphotype 537 Entoptychid Radiation 540 Phyletic Trends in Subfamily Geomyinae 542 Plio-Pleistocene Radiation of Geomyini 558 Morphotype 559 Specializations in Genera 560 Zygogeomys 564 Geomys 565 Orthogeomys 568 Pappogeomys 569 LITERATURE CITED 572 INTRODUCTION