NO. 4 TLANKTONIC FORAMINIFERA — CIFELLI 9 



and its fauna was identical with that of the Sargasso Sea. The 

 boundai^y is transitional in faunal character and contains a mixture of 

 Glohigerina and subtropical species. The mixed character of the as- 

 semblage strongly suggests that mixing of surficial waters occurs 

 across the Gulf Stream and that the subtropical species occurring 

 with Glohigerina in the slope waters are expatriates. 



Seasonal changes in faunal composition. — Clearly, seasonal cycles 

 cannot be described, nor, even, can the fact be established that such 

 cycles exist on the basis of only four seasonal traverses. However, 

 some marked changes were observed in composition of the subtropical 

 fauna from traverse to traverse and there can be no doubt that some 

 species of that fauna undergo considerable changes in relative fre- 

 quencies throughout the year. The most remarkable change noted 

 was the sharp increase of Globorotalia truncatulinoides in the winter. 

 Mostly rare or absent in the spring and summer stations, that species 

 showed some increase in the fall and was dominant in the winter when, 

 at one station (II), it occurred at a frequency of 55 percent. This 

 winter increase in Globorotalia truncatulinoides was mainly at the 

 expense of Glohigerinoides species (mostly G. ruber and G. trilobus 

 trilobus), which were relatively rare then but were dominant or im- 

 portant elements of the subtropical fauna at the other seasons. Pul- 

 leniatina ohliquiloculata also showed a considerable increase in the 

 winter. Globigerinella aequilaferalis attained its highest frequency in 

 the spring (60 percent at station 2) but remained fairly common 

 through all the seasons. 



It is more difficult to determine whether changes in frequencies of 

 species occur throughout the year within the temperate Glohigerina 

 fauna because of the considerable lateral changes in frequencies that 

 occur from station to station and also, possibly, because of the 

 morphologic variation of the Glohigerina species, which are sometimes 

 difficult to separate. The indications are that the relative frequencies 

 of the Glohigerina species are fairly stable throughout the year except 

 for Glohigerina aff. quinqueloha, which appears to increase appreciably 

 in the winter. 



SYSTEMATICS 



Since the primary purpose of this work was to determine the dis- 

 tribution of planktonic Foraminifera in a limited sector of the North 

 Atlantic, no attempt is made to treat the species monographically. 

 Only the original and a few pertinent references are given in the 

 synonymies. Extensive synonymies can be found in the works of 

 Cushman, Todd, Parker, and others. 



