A. J. Shearshy — On Operciilate Corals. 549 



is flat both horizontally and longitudinally; on the other hand, in 

 B. interpunctatum the ventral surface is convex longitudinally. 



It is also easily distinguished from B. nustrale, Eth. fil., by its 

 greater size and more deltoid shape and because the ventral surface 

 of B. australe is convex in longitudinal section. 



It is distinct also from B. enorme,^ Eth. fil., being much smaller in 

 size, more deltoid in shape, and the dorsal surface possessing a higher 

 degree of convexity. The vesicles in B. robiistum are also much 

 smaller. 



It differs from B. yassense,'^ Shearsby, in which form the apical 

 angle is obtuse and the upper portion of the ventral surface is convex, 

 being turned in towards the calice. 



I have not yet been successful in my endeavours to find an 

 operculum of this species. 



Locality and horizon. — Impure limestone on the Wargeila road 

 about half a mile west of Yass Junction Railway Station ; Upper 

 Silurian. 



Collection. — A. J. Shearsby. 



In the accompanying Plate XXVI, illustrating this paper, I have 

 given lateral views of the three other described species found at 

 Yass. The convexity of the ventral surfaces (v) of B. australe 

 (Fig. 8) and B. interpunctatum (Fig. 15) is here well shown in 

 comparison with the flat ventral surface of B. robustum. The acute 

 angle between the operculum and ventral surface of B. interpunctatum 

 is also clearly illustrated. 



Fig. 7 is an outline of a median perpendicular section of B. yassense, 

 wherein is depicted the inturned ventral margin of that species. 



Operculum, exothecal processes, and calicinal gemmation of 

 B. interpunctatum, De Kon. (Figs. 12, 12a). 



In his description of this species Mr. E. Etheridge, jun.,^ mentions 

 that the operculum was unknown, and states that the total apparent 

 absence of exothecal structure in B. interpunctatum showed a departure 

 towards Calceola, in which genus there is no trace of them. I have 

 succeeded in collecting a very large number of this species of 

 Bhizophylhtm, and several of the specimens have the operculum 

 in situ ; in addition to these a few detached opercula have rewarded 

 my search. 



Figs. 9 and 11 (Plate XXVI) show a corallum with the operculum 

 closed. Figs. 17 and 18 illustrate a fine and almost complete 

 specimen showing the corallum with its operculum widely opened. 



The operculum is semicircular and thick, concavo-convex. The 

 upper or outside surface is convex, and is sculptured with concentric 

 bands or lines of growth. The under or inner surface is concave, 

 with a stout median ridge starting from the straight hinge-line, and 

 projecting only about half-way across the surface. Near the hinge 

 where the ridge is stoutest is a small, deep, pit-like, triangular 

 depression, into which the counter septum fits when the operculum 



• Rec. Geol. Surv. N.S.W., vol. vii (1903), p. 232. 



2 Proc. Linn. Soc. N.S.W., pt. iv (1904), p. 869. 



3 Eec. Aust. Museum, vol. i (1891), p. 203. 



