GEOGRAPHICAL DISTRIBUTION. 139 



character of the plants ; and it is likely that both of 

 them have their influence. The mechanical properties 

 of the soil also have an influence, as in the instance of 

 sand, to which we have alluded. So too, a soil composed 

 of stifi" clay which on a few hours exposure to the sun 

 becomes baked and rigid, and cannot be penetrated by 

 them, is equally unfavorable. There are other localities 

 where individuals multiply infinitely. Mr. Anthony, of 

 Cmcinnati, Ohio, informs us, that in his walks around 

 that city, himself and a fi-iend collected during a single 

 week, above five thousand specimens of Helices, the time 

 devoted to the walks bemg taken from the mtervals 

 between business hours, and good and mature specimens 

 only being selected. Professor Adams states that he 

 collected, in one hour, more than one thousand specimens 

 of Helix minuscula ; and Dr. Gould found Bulimus 

 liibncus so abundant upon Oak Island, that many hun- 

 dreds could be taken from the ground with a single 

 handful of decaying leaves. 



Although some few species seem to occupy somewhat 

 Hmited localities, not having as yet been found over any 

 very broad region, yet the range of most species is very 

 extensive ; and, what is worthy of remark, the widest 

 distribution is to be noticed in the smallest species. The 

 smaller species are also tenfold, and probably a hundred- 

 fold more numerous than the larger. This circum- 

 stance is somewhat difficult of explanation. Both their 

 number and their broad range may perhaps be owing 

 to their very diminutiveness, on account of which they 



