Morphology of the Madreporaria. 



235 



several species, in addition to Lopliophyllum proliferum ; in 

 fact, wherever the specimens have been such as to admit of the 

 proseptal stage heing determined six septa have been revealed. 

 Streptelasma rectum, Ilall, is a species of wliicli examples are 

 fVcqiuMitly obtained having- perfect tips, and the whole 

 coral Inin ])rescrved in such a way that tiie septal develop- 

 ment can be followed throuj^hout. All the principal stages 

 have been described and figured in my paper on the Fossula, 

 and in the present connection the fact of supreme interest is 

 that six primary septa occur, all of equal size and situated 

 at equal distances apart [1. c. fig. 2). It may be mentioned 

 that in one specimen of S. rectum, only five primary septa 



The same number of septa occur withiu the middle primary chamber 

 (a, c) as within the ventro-lateral chamber («,, c). In the sub- 

 sequent growth all the entosepta become free from the central mass, 

 and the exosepta become free from the entosepta. 



were present, and the later septa were added in an order 

 different from that o£ the examples with six primary septa. 

 Manifestly one must be prepared for irregularities in the 

 septal formation of fossil corals just as much as in living 

 corals. 



Coralla of Cyathaxonia cynodon, E. & H., are also well 

 adapted for the determination of the number of primary 



