88 Proceedings of the Royal Society of Victoria. 



occupy about one half the visceral cavity ; they are small, vesicular 

 and arranged obliquely downwards. The tabulifi ai^e numerous, 

 incomplete, and vesicular in disposition, those towards the centre 

 of the calice being generally horizontal, whereas those next to the 

 dissepimental area are oblique in arrangement. Primordial 

 septa indistinctly seen in some cases ; the septa are slightly 

 thickened by stereoplasma. 



I do not think that this form can be confounded with any 

 hitherto recorded from Australian rocks, or with any with 

 which I am acquainted from foreign deposits. 



From C. S7vee^i, Eth. hl.,^ from Reid's Gap, Queensland, it 

 may be readily distinguished by the general appearance of the 

 septa, the less marked counter septum, and the absence of distinct 

 twisting of septa at the centre. There are several undescribed 

 forms from the Upper Silurian of Yass that approach closely to 

 C. mansfieldense. 



Family — Petraiadfe. 



Genus — Petraia, Munster, 1839. 



(Beitrage zur Petrefaktenkunde, i., p. 42.) 



Petpaia, sps. ind. 



(PI. III., Fig. 7, 8). 



Under this heading are included some imperfect internal casts 

 of rugose corals from Kilmore and Manstield. These show the 

 spaces occupied by short septa, longer at the base of the calycinal 

 cup, and almost vanishing towards the mouth, and apparently 

 alternately long and short. There is no trace of tabulate or 

 dissepimental structure. 



The genus Petraia includes corals characterised by the absence 

 of tabula? and dissepimental tissue and septa well-marked at the 

 base of the calice, but represented by folds at the top. Some 

 authors do not appear to recognise the validity of this genus, and 

 though doubtless it has been abused, still of late years the general 

 opinion appears to be changing, and some of the leading writers 

 on Palaeozoic Actinology give it due rank as a genus — Roeraer,^ 



1 Procs. Linn. Soc, N. S. Wales, 1S9d, ix., p. 521, t. 40, f. 3, 4 ; t. 41, f. 1. 



2 Lethaja Geognostica, 1SS3, i.. Lief. 2., p. 410. 



