The tests of 18 benthonic and one planktonic species of modern Foraminifera from 8 bottom samples recovered from the eastern Canadian shelf fall into two, or perhaps three groups with respect to mean mole percent MgCO3, as follows: Group 1 - 0 to 2.5 % MgCO3 ; Group 2 - 2 to 5 % MgCO3; and Group 3 - 5 to 9 % MgCO3 . The watermass characteristics and depth of each population are: Upper Water mass, -1 to 3 or 5 C, 33 o/oo salinity, 62 m and 73 m: Intermediate Watermass, 0 C, 34 o/oo salinity, 99m; and Deep WatennasB, 4 to 5 C, 35 o/oo salinity, 263 n, 431 m, 475 m, 479 m and 509 m.
In the samples examined low magnesium forms (Group 1) occur in all three water-masses and in a late-glacial beach sample. The intermediate magnesium form Ephidiella arctica (Group 2) and the high magnesium form (Group 3) Quinqueloculina arctica and 0. seminulum occur in the Upper Watermass. Populations of the low magnesium species Buccella inusitata, Islandiella helenae and Nonionellina labradorica are each found in both Upper and Deep Watermasses. The low magnesium value of Quinqueloculina stalkeri may indicate that the form should be placed in another genus.