THE NAUTILUS. 99 



creeks, at least during part of the year, which means the destruction 

 of nearly their entire faunas, the drainage of swamps, ponds and 

 lakes. Over large parts of Ohio, e. g., there are at present probably 

 less than twenty, or ten, per cent, of the number of mollusks which 

 populated them fifty or seventy years ago. 



And yet it appears that the effect on certain species is rather to 

 the contrary, and some have become common, or even abundant, at 

 some places under changed conditions. The following are examples: 

 Vallonia are not common in the forest, even rarely found there, but 

 are more frequent in the open, among grass, etc. V. pulchclla, ex- 

 centrica and costata are common, e. g., under old bricks, board*, etc., 

 in stone heaps, in towns and cities. V. excentrica is living in count- 

 less numbers in lawns which are regularly sprinkled, e. g., at Pitts- 

 burg, collected by Mr. Geo. H. Clapp, and at Cleveland, by Mr. J. A. 

 Allen. A single house lawn is populated by more individuals than 

 there were on a thousand acres of original forest. In lawns at Hud- 

 son, O., V. pulchella and excentrica are common, as found by Dr. 

 Rush, and there associated with Vertigo pygmcea Drap., which is 

 decidedly rare in Ohio. Zonitoides minusculus is common at many 

 places, under bricks and stones, in company with Vallonia, and Bifi- 

 daria procera Gld. I have found common in an old brickyard at 

 Washington, D. C., and under limestone slabs at Cincinnati. 



Gostrodonta ligera, generally not frequent in the woods, at least in 

 eastern Ohio, is common and often abundant, e. g., on railway 

 embankments, especially among dense plant growth, like Saponaria 

 officinalis, and, as cited elsewhere, it was found abundant along 

 garden walls and in thickets near houses in Kentucky. Patula stri- 

 atella (Pyramidula cronkhitei anthonyi), rare in the forest, is occa- 

 sionally found in large numbers under bricks, stones, old boards and 

 garbage material, in contrast to P. perspecliva, which is strictly con- 

 fined to the forest, and becoming rarer. Agriolimax campcstris is 

 now common in yards, gardens, around buildings, etc., and wherever 

 A- agrestis is introduced it is found in largest numbers at just such 

 places, while in Europe it has long been a pest to garden and field 

 cultures. Also in Europe the largest numbers of existing Limax 

 maximus L. are in cellars of houses, in greenhouses and similar 

 places, and so it is in this country where the slug is introduced. 

 Immense numbers of Pupoides marginatus, doing considerable dam- 

 age to strawberries, and Veronicella, destructive to tomato plantations 



