THE AMERICAN NATURALIST [Vol. XLIV 



able that the missing year 1901 would have furnished a 

 higher maximum than 1902, and that in some future 

 year the high average of 1902 may again be attained. 



10. Dense and Sparse Population Compared. — Two 

 lots of shells collected in 1899 deserve a separate para- 

 graph. They represent the extremes among all the lots 

 collected with respect to the density of the population. 

 They came from localities on the eastern shore of Buz- 

 zard's Bay about five miles apart and were collected 

 during the same week. 



TABLE XI 





^ No. ' 1 A.M. 



- 





Quisset-to-West-Shore 

 West Falmouth 



862 60.464 

 1,000 1 59.091 





±.0507 

 ±.0297 



The Quisset-to-West-Shore lot was gathered over an 

 area extending fully a mile along the rocky shore and 

 they were so scarce that it was necessary to utilize the 

 low-tide period of two successive days in order to ob- 

 tain them, and even then only 862 were obtained instead 

 of the usual 1,000. The West Falmouth lot, on the con- 

 trary, were all taken within a few minutes from a single 

 rock about five feet in diameter without by any means 

 exhausting the supply. 



It may be that the latter, as would be inferred by their 

 proximity, were more closely related to each other than 

 were the former, and consequently they might be ex- 

 pected to present less variation, or it is possible that the 

 Quisset-to-West Shore lot— representing the pioneers 

 or survivors in an apparently inhospitable area— suc- 

 ceeded in maintaining themselves because of their 

 greater variability {i. e., adaptability). Certain it is, at 

 any rate, that they represent the greatest variability 

 (standard deviation) of any lot of shells obtained from 

 the Atlantic coast except a thousand from West Shore 

 in August, 1902, and those already mentioned from 

 Staten Island. 



11. Variation of the Species TJro salpinx as a Whole. 

 —By combining the data of all the shells measured— a 



