20 



PROCEEDINGS OF THE NATIONAL MUSEUM 



Rarely the zonal lines become transformed into epithecal lines in 

 a portion of their length (Ceriopora aequipedis) . 



A zonal line is formed by divers elements, diapliragms, transverse 

 bands of vesicles, and at the intersection of the zooecial walls by 

 large vesicles with thicker walls. They correspond, therefore, along 

 the entire extent of their length to the tubes contracted and with 

 denser calcification. They may be only potential and manifested 

 only by simultaneous deformations of the tubes (Defranciopora) . 



Fig. 5.- 



-Ceriopora ovoidea, new species. A. Meridian section, X 16, through a zoarlum with definite 

 zonal lines. Lower Cretacious (Valangian): Sainte-Crok, Switzerland 



We are ignorant of the significance of the zonal lines. They per- 

 haps correspond to the arrests of growth occasioned by the seasons- 

 Their arrangement in the ensemble of colonial architecture seems to 

 be more a question of mathematics than of biology. 



Zooecial walls. — The walls of the tubes are very variable in thick- 

 ness and in structure, characteristics which determine the species. 

 Two difi^erent species have always a different vesicular constitution. 



