part 3] 



THE KELESTOMiy.E. 



207 



Generally the Kelestomiiiae conform to these common rules. It 

 is in the emphasis that they lay on particular applications of some 

 •of these rules that they are peculiar. The structures mainly 

 affected in the Kelestomine evolution are (1) the apertural bar; 

 •(2) the apertural spines ; (3) the interoecial secondary tissue : and 

 (4) the number of costae. The first two are correlated and are 

 most important, concerning, as they do, both genera fundamentally; 

 the third also concerns both genera; and the last behaves somewhat 

 •differently in Kelestoma and in Mmphasmopora. 



It is, therefore, possible to reconstruct a hypothetical Primitive 

 Kelestomine from which both Kelestoma and Morphasmopora 

 may be derived. Such a form, dia grammatically represented in 

 iig. 2, is considered to have the following characters : — the 



Fig. 2. — Diagram of a hypothetical Primitive Kelestomine. 

 X about 133 diameters. 



Distal apertural spine. 



Aperture. 



Avicularium. 



Proximal apertural spine. 



Avicularium. 



Distal fork of apertural 



bar. 

 Proximal fork of apertural 



bar. 



- Pelmatidium. 



Costa. 



Extraterminal front- wall. 



Termen. 



asty is incrusting and unilaminar ; the cecia are dimorphic ; the 

 normal cecia are about "5 mm. long, about '3 mm. wide, and 

 elliptical in shape ; there is a fair amount of secondary interoecial 

 tissue ; the costae are about ten in number ; each half of the 

 .apertural bar is bifid in a more or less vertical plane, and the upper 

 prongs of each half fuse one with the other, as do those of the lower 

 half; the number of the apertural spines is reduced to four, and 

 the proximal pair are considerably enlarged ; their distal ends 

 .approach or even unite with the fusion of the upper prongs of the 

 apertural bar ; the aperture is normal in shape ; the avicularia are 

 definitely arranged in one or more pairs on each side of the aperture 

 •of every normal cecium. 



it 2 



