Study of the biology, ecology, and shell construction of living large calcareous foraminifers provides data for comparison with fossil foraminiferal shells and permits biological interpretations of some fossil shell features, particularly growth rates, variations in growing seasons, and length of time to reach reproductive maturity. In living foraminifers variations in height, depth, and volume of individual chambers and in thickness of spiral wall relates to variations in available nutrients during the life span of the protozoans. Variation in nutrients usually correlates with seasonal variations in temperature and sunlight. The living large calcareous foraminifer Marginopora vertebralis lives two to more than five years before undergoing reproduction.

Comparison of shell morphological data from living foraminifers with data from extinct fusulinaceans indicates that three species of early Permian schwagerinid fusulinaceans lived four to more than seven years before reaching reproductive maturity. In addition two species, Schwagerina silverensis and Pseudoschwagerina robusta, from southwestern U. S. had two unequal seasons of maximum growth per year and the other species, Eoparafusulina yukonensis, from northwestern Canada had only one nearly uniform season of maximum growth per year. This suggests that during early Permian time southeastern Arizona and west Texas were located within the solar tropics or in an area where seasonal displacement of water currents carried unequal nutrient supply and that northern Yukon Territory was located outside the solar tropics or perhaps in the path of a nearly uniform seasonal current.

The regularity and size of megalospheric proloculi and microspheric juvenaria of fusulinaceans suggest these structures were formed prior to their release from the parent shell and may be compared with embryonic apparati of Recent Marginopora vertebralis. The young fusulinacean individuals may have developed in the tunnel prior to re