234 



Prof. J. E. Duerden on the 



rugose corals particularly adapted for investigating this 

 special problem. The number now available has enabled 

 me to demonstrate the presence of six primary septa in 



Fig. 9. — Cyafhaxonia cynodon (Septal Sequence, figs. 9-12). Section 



immediately above the tip, showing six primary equal septa, 



separated by six primary iuterseptal chambers. 

 Fig. 10. — The first pair of metasepla [a, a) has appeared, a septum within 



each of the middle interseptal chambers. 

 (In the next section a corresponding pair of meta^epta is seen within the 



ventro-lateral chambers: cf. fig. 4, a^, a,, and iig. 11, a„ a,.) * 



An additional pair of septa has appeared within the two middle chambers 

 (6, h), and also within the two ventro-lateral chambers (i,, 6,). 

 Certain of the exosepta (.r) are also present. 



(In the next section a pair of septa (c,, c,) is developing witliin the ventro- 

 lateral chambers in advance of the corresponding pair within the 

 middle chambers.) * 



* [The figures intended to follow fig. 10 and fig. 11 were not found 

 amono- the drawings forwarded by Prof. Duerden. I have added these 

 notes to explain the points that should have been illustrated by the 

 missing figures. — S. J. H.] 



