550 A. J. Shearsby — On Operculate Corals. 



is in its place. In several specimens in my collection the insertion 

 of the counter septum in this depression when the operculum is 

 closed is well shown. Besides possessing the stout median ridge, 

 the under surface shows traces of lateral septal ridges. Fig. 12 

 shows these faintly, but Fig. 12a exhibits the granular radiating 

 nature of the ridges more distinctly. 



Fig. 18 is a lateral view of a corallum with operculum in situ and 

 widely opened. In this figure will be noticed the thickness of the 

 operculum at the hinge-line, and the projecting nature of the median 

 ridge. 



Axothecal processes. — Although some scores of these interesting 

 corals have passed through my hands, I have found in only a couple 

 of instances traces of rootlets or anchoring stolons. In both of these 

 the extreme apex of the ventral surface bear two or three very small 

 knobs or protuberances. These being so delicate is no doubt one of 

 the reasons why a complete specimen with rootlets is so rare. 

 Another reason is the apices of the majority of the corals found are 

 missing. One small species of Rhizophjilnm which I presented to the 

 Australian Museum some time ago exhibits the exothecal processes 

 very clearly, showing as it does at the latei'al angles four little 

 knobs, two on each side of the apex. Fig. 16 is a specimen of 

 B. interpnnctatum from Hatton's Corner, which, besides showing 

 a budding tbrm, has two protuberances on the middle of the ventral 

 surface which may be the remains of rootlets. This is the only 

 specimen I have found which shows them in this position, so I am 

 figuring it for future reference. 



Calicinal gemmation. — Many of the specimens which I have 

 collected at Hatton's Corner show very distinct calicinal gemmation. 

 In all of tliese the young form has completely filled the calice of the 

 parent corallum. Examples of two of these are figured in PI. XXYI, 

 Figs. 13 to 16. The latter one is of special interest on account of 

 exhibiting, as mentioned above, what appear to be remains of the 

 exothecal processes or anchoring stolons. 



Locality and horizon. — Hatton's Corner, Yass ; Upper Silurian. 



Collection. — A. J. Shearsby. 



Further note on tue Exothecal Processes of Rhizophyllvm. 



Pi'evious to sending away the foregoing paper I made a minute 

 and lengthy search in places where I knew these corals aboinided in 

 order to obtain more complete information as to the occurrence of 

 rootlets on both species; but in spite of over a hundred specimens 

 passing through my hands I was unsuccessful. 



It was only about a week after the paper was sent away that 

 I visited a l)ed of impure coral limestone at Derrengullen Creek, 

 a few hundred yards above the crossing-place of the Yass-Wargeila 

 road, and found amongst numerous other Corals and Brachiopods some 

 fine specimens of R. rohustum, R. interpnnctatum. and R. atistrale, 

 Eth. fil. In my description of iZ. rohnstum I stated that no traces of 

 anchoring stolons or rootlets were visible, the Beekite rosettes 

 tending to destroy any trace of them. One of my specimens from 



