IOWA ACADEMY OF SCIENCES. 35 



through the fossiliferous loess as are some of the Succineas 

 and other terrestrial forms. Considering them rare in the loess 

 the author collected a number out of all proportion to the ratio 

 which actually exists between them and the terrestrial forms. 



The great majority of the specimens are L humilis Say. 

 Mingled with this species, and not always distinguishable from 

 it and from each other, are L desidlosa Say, and L cwperata 

 Say. All these species are rather small compact Limncece, such 

 as chiefly characterize our pond air-breathing molluscan fauna 

 of to-day. The first two species may be found creeping about, 

 in and near springs, streamlets, and small ponds, in all the 

 region covered by the loess, and L. humilis especially is quite 

 as frequently found out of the water as in it. Both are abund- 

 antly developed in ponds and streams which are dry during the 

 greater part of the summer. L. co/perata is also a common 

 species to-day, and like the two preceding species is often 

 found in ponds w; ich are dry during most of the year. Near 

 Lincoln, Neb., this species is common in prairie-ponds which 

 usually contain water for but a few weeks in the spring, and 

 last summer the author found it abundant upon the Sioux 

 Quartzite exposure in northwestern Iowa in a pool which con- 

 tained scarcely a gallon of water. It is noticeable that these 

 recent prairie specimens are of the small "depauperate " type 

 which occurs in the loess. Neither the habits of these species 

 nor their distribution in the loess indicate the presence of any 

 large bodies of water. They could be much more abundant 

 and yet could not form as conspicuous a part of the fauna of 

 the loess as the same species do of the fauna of our compara- 

 tively dry weather prairies to-day. 



The larger L. reflexa and L palustris mentioned in the table, 

 while locally common in larger ponds and prairie swamps 

 to-day, have not been found in the loess of Iowa and Nebraska. 

 They, too, are air-breathers, and never occur in deep waters. 



Physa — Two specimens are in the collection, one from Iowa 

 City, and one from Lincoln, Neb. Both are young and the 

 species cannot be satisfactorily determined. Two species have 

 been reported from Missouri by Swallow {I c p 215), but rep- 

 resentatives of this genus are evidently very rare. The habits 

 of all are essentially the same as those of the Limncece. 



Bulinus. — One species, B. hypnorum, has been reported from 

 Missouri by Swallow {I. c). It has not been found in the loess 

 of Iowa and Nebraska. The species is found now in prairie 



