IOWA ACADEMY OF SCIENCES. 105 



were subjected to extremely desiccating conditions, were found 

 after this experience, creeping about in their prison, seemingly 

 perfectly contented. Yet we are sometimes told that the 

 Succineas are all "semi-aquatic," or that they must have an 

 abundance of moisture. Another illustration, equally striking, 

 is furnished by the writer's experience and observations at 

 Council Bluffs during the past summer and autumn. It had been 

 purposed to make a detailed comparative study of the fossil 

 and modern molluscan faunas of that vicinity, but the work 

 was somewhat interrupted by the severe September rainstorms 

 and November blizzards. Nevertheless interesting and valu- 

 able data were obtained, and are here briefly presented. 



More than 4,000 fossils were collected, and their distribution 

 was carefully noted, in twenty exposures, beginning at the 

 eastern extremity of Fifteenth avenue in Council Bluffs, thence 

 along the bluffs to the high school, — a distance of about one 

 mile, — and in Fairmount park, along its winding roads, for about 

 half a mile eastward. The location of the several exposures is 

 shown on the accompanying map. A list of the fossil species, 

 together with the number of specimens collected in each 

 exposure, is given in the appended table. 



If this table is studied it will be observed that of the thirty 

 species collected, not one is aquatic. 



For purposes of comparison the writer made collections of 

 recent shells in seven distinct localities in practically the region 

 containing the above-noted exposures. These localities are 

 here discussed in detail, the letters designating them being also 

 employed to mark them on the map. 



A. A grassy, treeless hillside in Fairmount park, nearly 



opposite Eleventh avenue, and at an altitude of from 

 175 to 245 feet above the river valley.* Species 8, 11 

 and 29 f were found living. 



B. A grassy, treeless slope just above the exposure marked 



N. Altitude about 200 feet. Species 8, 10, 11, 15 and 

 29 were found. 



C. Near the Tenth aven le entrance to Fairmount park, at 



an altitude of about ninety feet above the river plain. 

 Species 8, 10, 11, 21, 22, 27 and 30 were found. A 

 few stunted and scattered Bur-oaks grew on the slope 

 immediately above this point. 



*The altitudes were all determined by barometric measurements taken from the 

 nearest north and south street on the river flat. 



+ The numbers refer to the species named in the table of fossils. 



