262 



BULLETIN "77, UNITED STATES NATIONAL MUSEUM. 



section, they are seen to extend completely around the cavity, or 

 nearly so, as shown in figure 154 a. 



Fig. 153. — ESTHONIOPORA COMMUNIS, a, TANGENTIAL SECTION, X20, SHOWING NORMAL ZOCECIA IN THE 

 UPPER aVLF, AND THE SMALL, THICK-"WALLED, MESOPORELIKE CELLS IN THE LOWER PORTION; b, VER- 

 TICAL SECTION OF THE SAME SPECIMEN, X20, WITH THE FREE ENDS OF THE DIAPHRAGMS BENT DOWNWARD; 

 C, A ZOCECIAL TUBE OF THE SAME SECTION, X20, SHOWING FURTHER MODIFICATION OF THE DIAPHRAGMS; 

 d, VERTICAL SECTION, X20, PASSING THROUGH A TRUE ZOCECIAL TUBE AND THROUGH TWO OF THE SMALLER 

 CELL OPENINGS OF THE BASE. GLAUCONITE LIMESTONE (B2), REVAL, ESTHONIA. 



Pig. 154.— Esthoniopora communis, a, tangential section, X20, cutting the semidiaphragms in 



SOME of the tubes; 6, VERTICAL SECTION, X6, THROUGH A SINGLE ZOARIAL LAYER; C, A PORTION OF 

 THE SAME, X20. KUCKERS SHALE (C2), BARON TOLL'S ESTATE, ESTHONlA, 



The peculiar form of growth mentioned in the specific diagnosis 

 above is shown in figure 1 55, while further interesting internal struc- 



