500 



THE AMERICAN XATURALIST [Yoi.. XLI 



ture of the night, rather than the maximum or the average. The 

 Fahrenheit scale is retained as given in the weather records. 

 The snails killed in formalin which were placed at the burrows in 

 this area are not included in the counts. 



in diameter, and the minimum nightly temperature, for a period of 



°F Occupied Empty To 



Apr. 



As in Table I it is seen that the number of empty shells was 

 never diminished, showing that once the empty shells were brought 

 to the surface they were not ordinarily moved again. Throughout 

 the seven weeks there is a steady increase in the number of empty 

 shells. If the last two columns be compared, it is observed that 

 on ten of the sixteen days the change in terni>cr:itnrc and tlie 

 change in the number of shells are of oj)p()sitc sign, - - that is, 

 with a rise in temperature shells are remoxcti and \uv \vv>:\. 

 These ten days include all the most marked tenipcianiiv clianges, 

 namely, those on Feb. 20, Feb. 27, Mar. S, and Mar. 27. >iniilar 

 to these are the changes for Mar. 1 and Apr. :i The ( (.nspiciions 

 exceptions are Feb. 24 and Mar. 31, when, though the temperature 



