SPIRE VARIATION IN PYRAMIDULA 

 ALTERNATA. 



FRANK COLLINS BAKER. 



I. Introduction. 



The object of the present investigation has been to ascertain 

 by quantitative means the amount of variation in the same spe- 

 cies of a pulmonate mollusk from several locahties. For this 

 purpose the shell of the common species, Pyramidula alternata, 

 has been selected, as that species shows a large amount of varia- 

 tion in the form of the shell, particularly in the height of the 



Among the mollusks little biometric work was done previous 

 to the year 1898. Since that time this group of animals has 

 been receiving marked attention and several exhaustive papers 

 have been published, notably those by C. C. Adams on lo and 

 C. B. Davenport on Pecten. These papers, however, have dealt 

 with marine or fresh water forms ; in this investigation the bio- 

 metric study has been applied to an air breathing land mollusk. 



11. Material. 



The material used in this investigation, Pyramidula alternata 

 Say, was secured from the following localities : 



1. Rochester, New York, on the steep hillside of the " Pinna- 

 cle " and the banks of the lower Genesee River. This locality 

 is heavily wooded and there is a large accumulation of fallen logs 

 and the ground is covered by a rich, black loam. Collected by 

 the writer. 



2. Auburn, New York, in damp, low, flat woodlands. Col- 

 lected by Dr. Howard N. Lyon. 



3. Bowmanville, near Chicago, Illinois, in flat woodlands. 

 The timber is large and heavy, the ground is strewn with fallen 



