34 



Study of X. obsoleta and N. triritfata 



REFERENCES. 



Apgar, A. C, 1891. MoUusks of tlie Atlantic Coast of the United Stjites, Soutli to Cai« 



HattcDus. Trciiton, New Jersey : Lucas and Co. 

 Batesox, W., 1894. Mateiial.s for the Study of Variation. London aiid New Vork : ^Lacmillan 



and Company. 

 Brewster, E. T., 1897. A Measure of Variability, and the Relation of Individnal Variations 



to Specific Difforences. Proc. Amer. Acad. Arts. and Sei., xx.xii., pp. 268-280. 

 Brewster, E. T., 1899. Variation and Sexual Selection in Man. Proc. Boston Soc. Nat. Hist., 



Vol. xxix., Xo. 2, pp. 45-61. 

 Bronn, H. G., 1862. Die Khussen und Ordnungen des Thier-Reiches, Bd. iii., 2. 

 Bdmpüs, H. C, 1898. The Variations and Mutationsof the Introduced Littorina. Zool. Bull., i., 



pp. 247-259. 

 CooKE, A. H., 1895. Molluscs. The Cambridge Natural Hi.story, Vol. in. New \'ork and 



London : Macmillan and Company. 

 Davexport, C. B., and .J. W. Blaxkixship, 1898. A Precise Criterion of Species. Science, vii., 



pp. 685-695. 

 DüNCKER, G., 1898. Benu'rkung zu dem Aufsatz von H. C. Bumpus "The Variations and 



Mutations of the Introduced Littorina." Biol. Centralbl., xviii., pp. 569-573. 

 GouLD, A. A., and \V. G. Bi.n'xey, 1870. Reiwrt on the Invertebrata of Jla.s.-iachusetts. Boston. 

 Mead, A. D., 1898. The Brecdiug of Aninials at Wooils Hol! iluring the nionth of April, 1898. 



Science, vii., pp. 702-704. 

 SiMROTH, H., 1891. Die Entstehung der Landthiere. Leipzig. 

 Tryon, G. W., Jr., 1882. Stnictural and Systeniatic Conchology. 



Verrill, A. E., 1873. Report on Invertebrate Animals of Vineyard Sound. Washington. 

 Walther, J., 1893. Einleitung in die Geologie als historische Wissenschaft. Erster Theil. 



Jena : Gustav Fischer. 



APi'KNÜIX A. 



Frequena/ Data. The class is designated both by a sorial iiumber and hy its middle 

 absolute value e.xpressed, in the case of length in millimeters, in the ratios of diameter to length 

 and aperture to length in percentages, in the case of angle in degrces, of whorls in units of one 

 whorl, of color iu percentages, and of dcpth of suture in units of one-liundredth of a millimcter. 

 1, 2, 3, and 3a, stand, as in Table L, for the lots of .V. obsoleta shells from locidities 1, 2, and 3, 

 and the N. Irivütata shells from 3, resijectively. 



Length: Localüy 1. 

 Cla.S8 ... j 



Froquency 



Class ... j 

 Frequency 



