part 3] 



THE KELESTOMIJM-:. 



217 



apertural bar fuse with the apertural spines ; but proximally there 

 is a deep cleft between the apertural spines and the apertural bar. 

 The eircum-apertural avicularia are not so highly raised as in 

 M. brydonei, are blunter in shape, more widely separated, and 

 directed proximally and towards the mid-line of the aperture which 

 they accompany ; and the patch of intereecial tissue that was inter- 

 calated in M. brydonei between the avicularium and the proximal 

 apertural spine on each side is extended to meet its fellow patch 

 across the distal ends of the apertural spines, so that the proximal 

 edge of the secondary aperture is formed of this strip of secondary 

 tissue with its long, tongue-shaped, median lacunae. Distal to the 



Fig. 12. — Diagram of ancestrcecium o/Morphasmopora 

 jukes-brownei. X abotit 175 diameters. 



Distal apertural spines. 



Aperture. 



Proximal apertural spine. 



Distal fork of spertural bar. 



Proximal fork of apertural bar. 



Pehnatidium. 

 Costa. 



Extraterminal front- wall. 



avicularia the distal edge of the secondary aperture is bounded, 

 as in M. brydonei, by two strips of secondary tissue meeting 

 in the mid-line, each containing a long, somewhat triangular 

 lacuna, so that each bears some resemblance to a much-elongated 

 avicularium. The intereecial secondary tissue has long, sinuous 

 lacunae. 



A comparison of fig. 11 (p. 216), representing the ephebastic 

 JHorphasmopora jukes-brownei, with Hg. 2 (p. 207), representing 

 the hypothetical Primitive Kelestomine, shows the extent to which 

 modification is carried in the former. 



