636 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
These septulae serve as in the Cheilostomata, for the passage of the mesenchyma- 
tous fibers. 
Fig. 197. — Structure of the cylindrical tubes. 
A. Longitudinal thin section, X 16, of a massive species Ceriopora vesiculosa new species. 
The walls are vesicular throughout their course. B. Transverse thin section, X 16, of Tretocy- 
cloecia dichotoma Reuss from the Helvetian of France. The tubes are of the same size at both 
the center and circumference. C. Longitudinal thin section of a ramose species Tretocycloecia 
reticulata new species, X 16. The interzooecial spaces are vesicular only at the extremity of the 
tubes. D. Portion of longitudinal thin section, X 60, of Heteropora constanti D’Orbigny, show- 
ing the great size sometimes attained by the vesicles. 
Cylindrical tubes or trepostomatous-like Cyclostomata . — In this division the 
inferior part of the tube is developed, but this part is very short. These tubes 
