part 3] 



THE KELESTOMIXJE. 



215 



VI. MoBPHASMOPOBA BBTDONEI Lang (fig. 10). 



The secondary aperture of KeJestoma is peculiar in appearance j, 

 that of Morphasmopora is almost grotesque ; that of the Primi- 

 tive Morphasmopora may well have had an intermediate appearance, 

 as suggested in fig. 9. From such a condition, the extraordinary 

 aperture of 31. brijdonei may have been evolved by the enormous 

 enlargement of the proximal apertural spines which impinge against 



Fig. 10. — Diagram of an cerium of Morphasmopora brydonei. 

 X about 133 diameters. 



Lacuna in secondary circum-apertural' 

 tissue. 



Aperture. 



Distal, exalted avicularium. 



Proximal, lowly avicularium. 



Lacuna in intercecial tissue intercalated 

 between the distal exalted aviculari- 

 um and the proximal apertural spine. 



Proximal apertural spine. 



Distal fork of apertural bar. 



Proximal fork of apertural bar. 

 Costa. 



Lacuna in intercecial secondary tissue. 



the distal forks of the apertural bar, but form fusions with them 

 only distally. On the proximal rim of the aperture, the apertural 

 spines remain separated from the pedestalled avicularia by a patch 

 of secondary tissue with a median lacuna. The distal apertural 

 rim is amalgamated with the secondary intercecial tissue sur- 

 rounding the aperture, and this has long slot-shaped lacunae ; thus 

 a long and a short pair of lacunae occur respectively on the distal 

 and proximal parts of the apertural ring. 



