THE NAUTILUS. 



Vor,. XVIII. FEBRUARY, 19O5. No. 10. 



SENSITIVENESS OF CERTAIN SNAILS TO WEATHER CONDITIONS. 



BY J. B. HENDERSON, JR. 



While collecting last summer about Cazenovia, N. Y., my atten- 

 tion was constantly drawn to the extreme sensitiveness to atmos- 

 pheric conditions of several species of land snails. I was surprised 

 to rind that upon some clear days collecting was excellent while 

 upon rainy days scarcely a living specimen could be found. 

 Puzzled by this failure of my expectations, I selected for special 

 observation a certain wooded hillside where the prevailing larger 

 types were Polygyra albolabris, tliyroides, dentifcra, Gastrodonta in- 

 tertexta, Omphalina inornata and fuliginosa. I visited the locality 

 from day to day keeping careful note of weather conditions. 



I found that the periods of greatest activity among these snails 

 were invariably marked by a falling barometer, but these periods 

 began considerably before there were any noticeable meteorological 

 symptoms presaging rain. At the commencement of actual rainfall, 

 the larger Zonitids only remained especially active. Towards the 

 close of a rain period (generally lasting from twelve to twenty-four 

 hours) though before definite signs of clearing were apparent, all the 

 snails disappeared, sometimes almost completely. The bright clear 

 days succeeding a rain epoch were always poor collecting days, even 

 though the woods were left damp and wet from the drenching that 

 only a Cazenovia rain can give. It would appear therefore, that 

 the moisture in the air rather than that upon the ground influenced 



