4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



have been discussed in a previous paper (Cifelli, 1962). Briefly, these 

 features may be summarized as follows : 



Abundance. — Considerable areal variation in numerical abundance 

 of specimens was observed, even between nearby stations. Some of 

 this variation is probably more apparent than real, since, in the 

 absence of a current meter, the actual amount of water filtered at the 

 towing stations is unknown, and the length of towing time is an inexact 

 and variable expression of this quantity. For the most part, however, 

 the differences in abundances between stations in the same water body 

 reflect the patchiness of distribution, a phenomenon that has long 

 been known to be characteristic of planktonic organisms. Patchiness 

 of distribution among planktonic Foraminifera has been recognized 

 in the Pacific by Bradshaw (1959) and Smith (1963). In general, 

 of the waters sampled the Sargasso Sea was the most uniform in the 

 abundance of specimens. 



The slope waters yielded the richest concentrations of specimens, 

 whereas the Sargasso Sea was generally impoverished. The shelf 

 waters were the most variable, and planktonic Foraminifera appear 

 to be rare and sparsely distributed at the inner part of the shelf. 

 Seasonally, the highest concentrations of specimens were obtained in 

 the fall and in the spring. The poorest concentrations were obtained 

 in the summer. 



Fauna! composition. — That the Gulf Stream is a boundary of 

 major biogeographic importance can be seen in the changes in faunal 

 composition of planktonic Foraminifera along the traverses studied. 

 On the shelf and inner slope the fauna is distinctly temperate in 

 character, being composed throughout the year almost exclusively of 

 species of Globigerina. The dominant species are Globigerina bulloides 

 and G. pachyderma incompta, but relative frequencies were found 

 to be variable and G. inflata and G. aff. qiiinqueloba are also common. 

 To the south Globigerina is replaced by a diverse subtropical group of 

 species that characterize the Sargasso Sea. The dominant subtropical 

 species are Globigerinoides ruber, G. trilobus trilohns, Globigerinella 

 aequilateralis, Globorotalia truncatiilinoides, and Piilleniatina obli- 

 quiloculata. The relative frequencies of these species, however, were 

 inconstant along the traverses and varied considerably throughout the 

 year. The position of the boundary between the temperate and sub- 

 tropical faunas also changed throughout the year but was always 

 observed on the north side of the Gulf Stream. It was closest inshore 

 in the fall and farthest offshore between winter and spring. Insofar 

 as could be observed, the Gulf Stream contained no endemic elements, 



