548 A. J. Shearshy — On Operculate Corah. 



During a recent collecting tour around Yass, I was fortunate 

 enough to find a large number of specimens of the genus Bhizophyllum, 

 amongst which were a new species which I am describing as 

 B. rohustum, and several specimens of B. inierpundatum, De Kon., 

 possessing the opercula in sittl. B. robustum makes the fourth species 

 of this genus which has been described from the Upper Silurian of 

 the Yass district ; and from fragments I have in my collection I am 

 of the opinion that there are several others which await determination. 



The following is a description of the new species : — 



Genus EHIZOPHYLLUM, Lindstriim. 

 Khizophyllum robustum, sp. nov. (PI. XXVI, Figs. 1-6.) 



Corallum simple, pyramidal, short, widely expanded above, acutely 

 pointed below, lateral angles rounded, section semicircular, plano- 

 convex. Dorsal surface convex ; ventral surface flat, both horizontally 

 and vertically. Calice semicircular, moderately deep ; dorsal margin 

 sharp and thin, slightly arched above the level of the ventral margin ; 

 ventral margin thick, horizontal, with well-marked central fossula. 

 Several thin projecting septa are noticeable on the ventral margin. 



A thick corrugated epitheca covers the corallum ; that on the 

 ventral side being partly replaced by minute rosettes of Beekite. 

 A portion of the ventral surface is broken away, and shows to 

 a depth of about a quarter of an inch the weathered vesicular 

 internal structure of the corallum. These vesicles have their convex 

 surfaces facing inwards and upwards. 



No traces of anchoring stolons are visible on the specimen, the 

 Beekite rosettes near the lateral angles naturally tending to confuse, 

 if not altogether obliterate, these processes. A small portion, 

 probably about a quarter of an inch, of the apex is missing, but 

 otherwise the specimen is well preserved. 



The specimen exhibits a most interesting illustration of 

 rejuvenescence by calicinal gemmation ; about half of the calice of 

 the corallum being occupied by the upper portion of a young form, 

 which exhibits in a marked degree the same characteristics as the 

 parent form, with the addition of a sub-central depression in the 

 calice. (PI. XXVI, Fig. 4.) 



The measurements of B. robustum are as follows : — Parent corallum, 

 length of dorsal surface 1^ inches, length of ventral surface 1 inch. 



Note. — Both of these measurements may be increased by an 

 additional quarter of an inch, for, as mentioned previously, portion 

 of the apex is missing. 



Parent corallum, greatest diameter of calice l^ins., least i'm. 

 The measurements of the calice of the young form are : — Greatest 

 diameter xiin-j least | in., depth -rs-in. 



B. robustum differs from B. inierpunctatum, De Kon., by its much 

 greater size and particularly the manner in which the dorsal margin 

 rises above the level of the ventral, causing the angle made between 

 the operculum when closed to be obtuse; while in B. interpunctatum 

 the angle is acute on account of the dorsal surface being much 

 shorter than the ventral ; and also the ventral surface of B. robustum 



