8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



by random bends at ramose extensions of overgrowths beyond the 

 distal tips of primary branches, and irregular branch angles in lateral 

 secondary branches. The zoaria were further complicated by repeti- 

 tions of thin- and thick- walled growth in the outer region of the 

 exozone (mature region) without the formation of intervening basal 

 laminae. This apparently rejuvenated growth formed localized swell- 

 ings on the zoaria, and combined with adjacent patches of overgrowth 

 to form some of the secondary branches. 



Monticules. — Monticules are prominent tubercles. The apertures 

 of some monticular zooecia are restricted or closed by a distal thicken- 

 ing of the walls, and the walls and outer diaphragms of monticular 

 mesopores are somewhat thicker than those of surrounding mesopores. 

 Monticular mesopores generally contain one to several more dia- 

 phragms than intermonticular mesopores. 



Longitudinal View: Endozone. — In the endozone (immature or 

 axial region), zooecial walls are longitudinally laminated and do not 

 show the dark granularity that is common in the Trepostomata. The 

 zooecial walls range from undeviating to irregularly undulating. In a 

 few specimens the endozone is interrupted by a zone arching distally 

 across the branch that is marked by variable thickening of the zooecial 

 walls. Normal thin-walled zooecial growth generally continues distally 

 from the thickened walls of the arched zones with some bifurcating 

 but without other break. At apparently random levels within a colony, 

 some or all of the zooecia within the endozone have been eroded and 

 the tubes rilled with mud. Subsequent growth was initiated from 

 adjacent zooecia and the eroded areas were covered by a basal lami- 

 nation of the overgrowth that continued the colony distally. 



Exozone: Inner region of mesopores. — The boundary between the 

 endozone and exozone is defined by the points of origin of the 

 mesopores. The inner region of the exozone extends distally for one 

 to several mesopore diaphragms, but generally not more than four. 

 The mesopores begin proximally with walls and diaphragms that are 

 slightly thicker than the zooecial walls of the endozone. Mesopore 

 walls curve broadly through 90 degrees into transverse positions 

 relative to the length of the mesopores, thereby forming diaphragms. 

 The broad curving results in constrictions of the mesopores at the 

 positions of the diaphragms to form cystlike chambers. In this inner 

 region of the exozone, mesopore walls commonly are longitudinally 

 laminated, but many, especially the thicker ones, develop transversely 

 laminated structure, either intermittently or throughout their length. 



In the inner region, mesopore diaphragms regularly display centrally 



