100 Proceedings of the Royal Society of Victoria. 



posterior to the umbo the ligamental groove is long and narrow, 

 and is margined by a much more elongate but relatively broad, 

 .smooth, flattened, or sliglitly concave area, which is well defined 

 from the remainder of the shell by an angulation running from 

 the umbo to the posterior margin. The post-dorsal margin is 

 slightly arched, and joins the posterior margin somewhat suddenly; 

 ithe junction is usually convexly rounded, but occasionally a 

 distinct angulation is noticeable giving rise to a posterior 

 truncation. 



Ventral margin regularly and gently convexly rounded to the 

 more strongly convex anterior margin. The surface of the valves 

 is strongly marked by closely packed radial ridges, which 

 are broader than the interspaces umbonally, but the latter 

 become as broad at the ventral margin; the radial ridges show 

 .a tendency to subdivision by a minor i-adial groove, and this is 

 more especially noticeable on the anterior half of the shell ; 

 concentric lines of growth are also present and in conformity with 

 .some of these, are thin erect frills which are corrugated on their 

 A'entral aspect, the ridge on the frill corresponding in position to 

 the interspaces between the radial ridges. The frills become 

 more crowded towards the ventral margin. Inner margin 

 ^lenticulated, anterior denticles at first very fine, gradually in- 

 -creasing in size to the anterior portion of the ventral margin, 

 then along the median portion finer and fairly regular, thence to 

 the posterior a few very strong ones, then gradually fading 

 away. 



Di/ne/isions.-—Ty^& shell, antero-posterior diameter, 60 mm.; 

 aimbo-ventral diameter, 51 nnn. ; greatest thickness through one 

 valve about 18 mm. Other specimens range 65 mm. by 52 ram.; 

 63 by 49, 56 by 46, 53 by 42, 52 by 45, and a smaller specimen 

 with both valves in contact gives 44 by 35 and a thickness 

 through both valves of 24 mm. 



Locality. — Lower beds of the Spring Creek series or Bird Rock 

 Bluff, near Geelong. Jan Jukian, — Eocene. 



Observations. — Two species of this genus of a very similar 

 type of shell have already been described by Professor Tate, 

 namely — C. hormophora, and C. dimorphophylla. The former, 

 iiowever, is of different shape, is strongly inflated, and shows 

 many distinctive featunis in the surface sculpture ; the description 



