166 



BULX,ETIN 125, UNITED STATES NATIONAL MUSEUM. 



zone. Employing the known localities we have the following table for the Northern 

 Henaisphere : 



Species. Geolopcal distribution. Latitude. 



H. clavula Helvetian of Italy 45"^ 



Pliocene of Rhodes , 36° 



H. sandbergeri Aquitanian of Gironde 44° 



H. Tostrigera Upper Miocene of Virginia 37° 



Upper Miocene of North Carolina 35° 



Lower PUocene of South Carolina 33° 



Upper Pliocene of Florida 25° 



Recent of Florida 22° 



The interpretation of this table indicates in a striking fashion the rapid and 

 continuous descent of the Tropic toward the Equator. No species of the genus 

 exists in the faluns of Touraine (forty-ninth parallel) situated without the equitorial 

 zone. On the contrary, the Helvetian of Italy represented by H. clavula was nearer 



Fig. 30. — Genus Hippaliosina Canu, 1918. 



A-C. Hippaliosina rostrigera Smitt, 1872. A. Ordinary zooecia. B. Group with an ovicelled 

 zooecium. (A, B, after Smitt, 1872.) C. Interior of a fossil example, X 20. 



D. Hippaliosina sandbergeri Reuss, 1869. An ovicelled specimen, X 25, from the Aquitanian of 

 Leognan, France. 



E-H. Hippaliosina brevirostris Canu, 1918. E. Ovicelled specimen, X 25. F. Operculum of the 

 o\icelled zooecia, X 85. G. Operculum of ordinary zooecia, X 85. H. Areolar pores. X 85 (E-H 

 after Waters, 1889.) 



to it. This latter species does not exist in the more southern European Pliocene. 

 E. sandbergeri, not being able to emigrate toward the south probably by the obstacle 

 of a continental barrier, was exterminated in its place. It is probable that it will 

 be discovered in more northern Oligocene deposits. 



For the Southern Hemisphere this phenomenon is less evident because of the 

 imperfect geographic conditions. .Uthough the fossil species H. laxipora has been 



