36 IOWA ACADEMY OF SCIENCES. 



ponds in Iowa and Nebraska, and seeks the habitats which are 

 agreeable to Limncea palusiris. 



Planorbis. — Two sj^ecies have been recorded from the loess. 

 P. tvivolvis has twice been reported (see Table I), but in each 

 case with doubt. P. parvus (it may be P. dilatatus) is rare in the 

 western loess, five specimens only being in the collection. In 

 habits these species of Planorbis are all, like the species of 

 Limtioia and P/iysa, inhabitants of shallow water borders. 



Segmentina. — One species, ^S* armigera has been reported from 

 Missouri by Swallow. It is evidently extremely rare. The 

 species is now locally common, especiclly in prairie ponds, and 

 in habits is similar to Planorbis 



All of the foregoiag species are air-breathing, and all are 

 found living abundantly in Iowa and Nebraska to-day. Their 

 presence not only does not prove that there w^as an excess of 

 moisture, but their scarcity actually suggest that there was 

 less water than may now be found over the same areas. 



Valvatd. One species, V. trlcannat.a, has been reported from 

 Missouri (see Table I). This and Gamp'^lom i su'isolidicm are the 

 only branchiate aquatic Gasteropods reported from the loess.* 



It is now locally common in ponds and sluggish streams, 

 often being found in ponds which become dry in summer. Its 

 total absence from the loess of Iowa and Nebraska, and its 

 scarcity in Missouri, make the species of little value in deter- 

 mining prevailing conditions in loess times 



Pisidium. — Two valves only, of a species which has not been 

 satisfactorily identified f, were found at Iowa City, associated 

 with Limncea in the little pocket to which reference has already 

 been made. The species of Pisidium are small bivalves (hence 

 gill-bearing and aquatic), which are locally common in all our 

 fresh waters. They also frequently occur in ponds and stream- 

 lets w^hich become dry during the summer. For two reasons 

 the author collected numerous specimens of a species much like 

 our fossils (probably the same) near Lincoln, Neb , in a stream- 

 let which during both years was dry all summer. 



The presence therefore, of aquatic forms" of the foregoing 

 types does not indicate that large bodies of water, whether in 

 lakes or rivers, existed, — indeed it does not show that, even in 

 the particular localities where they were developed, water was 

 found during all the year. No doubt there was water. There 



*P0inatiopsi8 lapidaris and IJelicina occulta, both gill-bearing, but terrestrial in habit 

 are considered with the terrestrial forms. 

 +For Cyclas from Missouri see Table I. 



