TABLE OF CONTENTS. 



Page. 



Introduction 501 



Sketch of different classifications 501 



Anatomy of the Naiades 503 



Shell characters 504 



Geographical provinces 504 



Map of the Naiad provinces 505 



Number of genera and species 505 



Beak sculpture 507 



Past history of the Naiades 507 



Mutelidse 512 



X 



The work of Rafinesque 512 



The work of Lamarck 513 



The so-called "New School" 513 



Synopsis of the genera of Naiades 514 



Synopsis of the Naiades 516 



Family Uniohidse 516 



Subfamily Unioninae 516 



Heterogeuse 516 



Genus Truncilla 516 



Micromya 524 



Lampsilis 526 



Pseudospatha 577 



Hyriopsis 578 



Chamberlainia 582 



Cristaria 583 



Lepidodesma 586 



Pilsbryoconcha 587 



Medionidus 588 



Nephronaias 591 



Glebula 597 



Obovaria 599 



Plagiola 603 



Digen* 607 



Tritogonia 607 



Mesogeu;c 609 



Cyprogenia 609 



Obliquaria 610 



Ptychogeme 612 



Ptychobranchus 612 



Eschatigense 614 



v 



