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PALEONTOLOGY 



and less prominent than the others : it is called the 

 cardinal septum. The next major septa on either side are 

 nearly parallel, converging very slightly downwards on 

 the calyx-sides, and diverging slightly on the floor, where 

 they form the boundaries of the fossula. It is not easy 

 to make out any further characters of the septa in the 



CD 



FIG. 90. DEVELOPMENT OF MAJOR SEPTA IN A RUGOSE CORAL. 



i, 2, 3, Protosepta; a, b, c, metasepta ; i, cardinal and counter septa; 

 2, alar septa ; 3, counter-lateral septa. Seven successive transverse 

 sections, giving ontogenetic stages, are shown. The numbering and 

 lettering denote the order of development of the septa. (After Car- 

 ruthers and Duerden.) 



calyx, but by taking transverse and longitudinal sections 

 through the coral more may be learned. 



If a section were taken very near the apex of a well- 

 preserved specimen, it is probable (from what is known 

 in allied corals) that at the very early stage of growth 

 here preserved, six septa only would be present. Owing 

 to the destruction of the actual apex in most specimens 

 it is not possible to prove this, but these six primary 



