title: Secondary calcification in the foraminiferal genus globorotalia.
abstract: Populations of four species of the planktonic foraminiferal genus Globorotalia from sediments in the Gulf of Mexico show the effects of secondary thickening of the test. Quantitative tabulation of the distribution of thin- and thick-walled specimens illustrates an abrupt and separate depth at which the thickening takes place for each species.
authors.forename: W N
authors.initials: WN
authors.lastname: Orr