PLATE XXI. 



PAGE 



Pigs. 1-3. ViviPARus MARYLANDicus Clark 212 



Arlington, Maryland. 



Figs. 4-5. ViviPARus AKLiNGTONENSis Clark 212 



Arlington, Maryland. 



Fig. 6. Bythinia aeundelensis Clark 211 



Arlington, Maryland. 



Fig. 7. Unio patapscoensis Clark 213 



White House Bluff, Virginia. 



Figs. 8, 9. Cyrena marylandica Clark 213 



Arlington, Maryland. 



520 



