An UNDESCRIBED AUSTRALIAN CYSTIPHYLLID— 

 MICTOCYSTIS—vkou the UPPER SILURIAN ROCKS 

 of the MOUNT CANOBALAS DISTRICT. 



By R. Etheridge, June., Curator. 



(Plates iv.-v.) 



To Mr. C. A. Sussmilch, of the Technical College, Sydney, 1 

 am indebted for the loan of specimens, and presentation of others 

 to the collection, of a very interesting Cystiphyllid coral from 

 the Upper Silurian rocks in the neighbourhood of the Canobalas. 

 So far as Australian literature is concerned, it is certainly 

 undescribed. 



The essential feature of this coral consists of a mass of coarse 

 blister-like vesicular tissue surrounding a series of cylindrical 

 and parallel visceral chambers, apparently without mural invest- 

 ment other than the convex oblique surfaces of the vesicles in 

 question. On the upper or external surface of thecorallum these 

 vesicles have a very marked blister-like appearance and are not 

 traversed by radiating or geniculate septal costse at all. 



The visceral chambers are provided with numerous well- 

 developed lamellar septa which proceed almost to the middle of 

 each chamber, cutting through the horizontal tabulate centres ; 

 these septa are confined to the visceral chambers, and do not 

 in the least impinge on or pass over the blister-like vesicular 

 tissue ; again they do not appear to quite reach the calicinal 

 centre, nor can I distinguish any columelarian structures; indeed 

 there seems to be a small free central tabulate area to each 

 visceral chamber. The tabula? are on the whole complete, 

 although here and there lenticular vesicles are formed. 



The affinities of this coral form a difficult problem. In the 

 first place the vesicular tissue constituting the general mass is 

 essentially that of the Cystiphyllidse, blister-like vessels closely 

 superimposed on one another. Any further affinity with this 

 family can only be traced to some extent through Actinocystis, 

 Lindstrbm, and Mesophyllum, Schluter. In the former the 

 centres of the corallites are septate, but the septal areas small, 

 and I believe not tabulate ; the whole of the broad external zone- 

 being entirely vesicular in the usual cystiphyllid manner. The 

 \isceral chambers also appear to be formed in the same way as 



