IOWA CITY LOESS. 211 



Unio ^uteolus Lam. Quite common. 



Unio metanever Raf. Common. 



Unio obuouus Lam. Not common. 



Unio orbiculatus Hild. Rare. 



Unio parvus Barnes. Common. 



Unio pucatus Le S. Very common. 



Unio pustulosus Lea. Very common. 



Unio rectus Lam. Common. 



Unio rubiginosus Lea. Not rare. 



Unio securis Lea. Rare. 



Unio spatulatus Lea. Rather common. 



Unio TENuissimus Lea. Rare. 



Unio trigonus Lea. Very common. 



Unio tuberculatus Barnes. Very common. 



Unio undulaTUS Barnes. Quite common. 



Unio ventricosus Barnes. Very common. 



Unio verrucosus Barnes. Rare. 



Margaritana compl,anata Barnes. Common. 



Margaritana hildrethiana Lea. Locally common. 



Margaritana marginata Say. Rather rare. 



Margaritana rugosa Barnes. Quite common. 



Anodonta edenTula Say. Common. 



AnodonTa ferussaciana Lea. Not rare. 



Probably other species of Anodonta occur. 



A summary of the aquatic species here listed presents 

 the following results : 



Aquatic species found here both living and fossil . 5 



Aquatic species living here and occurring in the loess 



elsewhere ......... 7 



Aquatic species of the occurrence of which in 



undoubted loess no record exists . . , . .66 



Total 78 



It will be observed that the proportion of local aquatic 

 shells found in the loess, here or elsewhere, is compara- 

 tively insignificant, and what is true of species applies with 

 even greater force to individuals. The fossil shells of 

 aquatic species, with the two exceptions already noted, 

 occur very sparingly indeed. The writer's own sets of 

 these fossils, a part of the fruit of twenty years of careful 

 search, form such an insignificant part of his collection 

 that they seem scarcely worthy of serious attention. But 



