Sinistral Globigerina pachyderma (Ehrenberg) appears for the first time in the Deep-Sea Drilling Project site-36 section in the lower Pleistocene. The location of this site, 40°59.08^primeN lat., is within the Holocene transitional faunal zone for planktonic Foraminifera. From scattered occurrences in the lower Pleistocene sediments, this species gradually increases in abundance until, midway in the Pleistocene, it becomes a predominant element. This indicates that the boundary between the subpolar and the transitional water masses did not shift over the site-36 location until mid-Pleistocene time, thus bringing in subpolar faunas for the first time. The proportion of left-coiling forms to right-coiling forms is not always diagnostic in identifying cold cycles, nor d es it apparently give very good diagnostic data on the intensity of cold cycles.

Ontogenetic growth analyses on Pliocene dextral and sinistral forms often referred to as G. pachyderma by workers indicates that there is a fundamental difference between these forms and the sinistral G. pachyderma of the Pleistocene and Holocene. They are placed in Globorotalia pseudopachyderma Cita. Permoli Silva, and Rossi. Whether the sinistral form of this species was adapted to subpolar conditions is uncertain, and, in fact, some populations of this form seem to have lived in warmer waters than the dextral populations.

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