GENERAL DISCUSSION 5 



TABLE I. DISTRIBUTION OF FRESH WATER SHELLS NORTH 

 OF LATITUDE 49°, ACCORDING TO THE DRAINAGE 



SYSTEMS NOW EXISTING. — Continued. 



Name of Specif 



Ph ysa ampullacea 



Physa hordacea 



Aplexa hypnorum 



Ancylus rivularis 



Ancylus parallelus 



Ancylus fragilis 



Ancylus kootaniensis 



Goniobasis plicifera 



Amnicola limosa 



Amnicola pallida 



Amnicola eniarginata 



Amnicola cincinnatiensis 



Lyogyrus granum 



Pomatiopsis lapidaria 



Fluminicola nuttalliana 



Fluminicola virens 



Valvata tricarinata 



Valvata sincera 



Valvata lewisi 



Valvata var helicoidea 



Valvata mergella 



Valvata virens 



Carapeloma decisum 



Lampsilis ventricosus 



Lampsilis luteolus 



Lampsilis borealis 



Lampsilis radiatus 



Lampsilis ligamentinus 



Lampsilis rectus 



Lampsilis ellipsiformis 



Lampsilis alatus 



Lampsilis gracilis 



Strophitus rugosus 



Anodonta beringiana 



Anodonta oregonensis 



Anodonta nuttalliana 



Anodonta wahlamatensis 



Anodonta marginata 



Anodonta implicata 



Anodonta grandis 



Anodonta kennicotti 



Anodonta pepiniana 



Anodonta kennerleyi 



Gonidea angulata 



Anodontoides ferussacianus . 



Symphynota costata 



Symphynota complanata 



Margaritana niargaritifera.... 



