40 
PROFESSOR P. M. DUNCAN ON OUYNIA ANNULATA. 
Note. — March 25, 1871. 
Some days after this communication was sent to the Royal Society, Mr. J. Gwyn 
Jeffreys, F.R.S., forwarded me several specimens of Guynia annulata which he had 
found adherent by their sides to mollusca obtained from the Adventure Bank. These 
specimens are well preserved, and one of them shows the small commencement of the 
long cylinder of the coral. Others exhibit the columella and the large septa and the 
normal septal arrangement (octomeral). But one rather deformed coral exhibited on 
a fractured surface which was at right angles to the long axis six large septa instead 
of the usual eight : this of course required careful examination and explanation. The 
septa in the lower and therefore older part of the coral were clearly irregular in their 
growth ; but a section midway between this portion and the fractured part established 
the interesting fact that the lower part of the corallum possessed the normal octomeral 
septal arrangement, and that the upper, in consequence of the abortion of two septa, had 
the Neozoic hexameral type. This is very suggestive in the matter of the evolution of 
hexameral from octomeral types, or rather from the tetrameral. 
March 24, 1871. 
