166 
BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 
zone. Employing the known localities we have the following table for the Northern 
Hemisphere: 
Species. Geological distribution. 
H. clavula .Helvetian of Italy...:. 
Pliocene of Rhodes. 
H. sandbergeri . Aquitanian of Gironde.. 
H. rostrigera . Upper Miocene of Virginia. 
Upper Miocene of North Carolina. 
Lower Pliocene of South Carolina. 
Upper Pliocene of Florida. 
Recent of Florida. 
Latitude. 
. 45° 
.. 36° 
,. 44° 
. 37° 
.. 35° 
.. 33° 
. 25° 
,.. 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 
ovicelled 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. 
H. 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. Although the fossil species H. laxipora has been 
