48 



BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



crowded on the large walls (fig. 4. .4). When there is a mucro, the elements are 

 grouped in radial rows (fig. 4. /?). The walls of the mural rims in the Mala- 

 costega also have their elements grouped in rows perpendicular to the lines of 

 the zooecial sutures (fig. 4, C). The olocystal walls are always smooth (fig. 4, D) ; 

 they are perforated by very small pores when they are surmounted by a tremocyst 

 or a pleurocyst. 



Tremocyst. The frontal endocystal buds deposit above the olocyst a second 

 calcareous deposit called the tremocyst; the pores thus formed are the tremopores : 



Bx 100 



C x 100 



D x 20 



FIG. 4. Structure of the olocyst. 



A. Thin section through the basal wall of Jlembraniporiilra spissiinuralis, new species, X 100, 

 showing olocyst with crowded elements. 



B. Olocyst of AcantJiimiella oecioporosa, new species, X 100, with elements grouped in radial 

 lines. 



C. Thin section of Periporosella tantiUa ('ami and Bassler. 1917, X 100, exhibiting elements 

 of olocyst grouped in series around the mural rim. 



D. View of interior of Smittina anrnilnta Rtuss, ISO-i, X 20. showing the smooth olocyst, per- 

 forated by areolae only. 



the zooecia, which are provided with them, are tremogastres ; the tremopores are 

 funnel shaped or tubular : they are always traversed by mesenchymatous elements. 



The funnel-shaped tremopores arise from a very small pore perforating the 

 subjacent olocyst (fig. 5, ^1) ; they become enlarged at the exterior (fig. 5, B). 



The tubular tremopores or tiibulae also arise from a small pore piercing the 

 subjacent olocyst (fig. 5, ('), but the latter is very thin and permits one to see through 

 a circular, white area the base of the tubula itself. At the exterior the tubules have 

 the same diameter (fig. 5, D). 



Often the tubular pores are united among themselves and the number of the 

 interior pores (fig. 5, E) does not correspond to the number of exterior pores (fig. 



