NO. 4 PLANKTONIC FORAMIN'IFERA CIFELLI 2/ 



chamber there is a single supplementary aperture, in contrast to G. 

 ruber in which there are two supplementary apertures on the chamber. 

 This species shows variation in the size of the supplementary 

 aperture and in the development of the final saclike chamber. The fol- 

 lowing forms which are completely transitional were recognized in 

 the material studied. 



1, Supplementary aperture small, saclike final chamber lacking. 



2, Supplementary aperture large, saclike final chamber lacking. 



3, Supplementary aperture small, saclike final chamber present. 



4, Supplementary aperture large, saclike final chamber present. 



Form 1 occurs most commonly, but form 2 is also present in 

 appreciable numbers. Form 3 and particularly form 4 are relatively 

 scarce. The specimens agree very well and are identical with Miocene 

 topotypes of Glohigerina trilohus Reuss in the U. S. National Museum 

 collections, which include both forms 1 and 2, with dominance of 

 form 1. They differ from G. saccuUfer Brady in having smaller sup- 

 plementary apertures and less-developed saclike final chambers. Speci- 

 mens of G. saccuUfer from Recent Pacific bottom sediments studied 

 for comparison included the same range of forms as G. trilohus but 

 showed a dominance of forms 3 and 4. Moreover, the Pacific sac- 

 culifer includes a form with an elongate saclike final chamber (Brady, 

 1884, pi. 80, fig. 4) that was not observed in the North Atlantic 

 material. 



Thus, G. trilohus and G. saccuUfer represent overlapping parts of 

 a gradational series, a fact noted by several earlier workers, and as 

 such are distinguishable only at the subspecific level. Although called 

 subspecies, however, trilohus and saccuUfer are not subspecies in the 

 geographic sense of the neontologist, since G. trilohus sensu lato has 

 a long, complex fossil record. Additional difficulties in applying the 

 neontological subspecies concept are introduced by the fact that the 

 species has a pelagic habitat. The isolating mechanisms in the open 

 ocean are much less understood than those on land or even on the 

 ocean bottom. 



It would be convenient if the gradational series between trilohus 

 and saccuUfer also represented an evolutionary series, as then it would 

 be an easy matter to divide the series into vertical subspecies, in the 

 sense of the paleontologist. Unfortunately, such a simple phyletic 

 trend does not characterize this lineage. The present North Atlantic 

 assemblages show a closer morphologic affinity to the Miocene as- 

 semblages of trilohus than to Recent assemblages of saccuUfer. Thus, 

 G. trilohus will not yield gracefully to a vertical division of subspecies. 



