Older Tertiary of Victoria. 95 



rapid attenuation posteriorly, rather inflated in the neiglibour- 

 hood of the umbos but becoming depressed ventrally and 

 posteriorly. 



Umbo-post-ventral keel not always well defined, but when 

 present, concavely curved to the posterior margin, sometimes 

 an intermediate faint keel shows between the posterior 

 depression for the ligament and the undjo-ventral keel. Post- 

 dorsal margin deeply concave to a short straight posterior 

 truncation, thence regularly convex to the anterior and thence 

 somewhat straight to the umbo. Umbos strong and very tumid, 

 to flat and depressed at the crest, incurved anteriorly, and 

 strongly but not very closely corrugated, the flrst 4 millimetres 

 •of the beak bearing from 9 to 11 corrugations. Lunule very 

 large, deep and broad, being in length nearly one-half the umbo- 

 ventral diameter; posterior to the beaks deeply and broadly 

 ■excavated. 



Surface covered with fine, close, but irregular concentric lines 

 of growth very closely packed anteriorly and posteriorly, about 

 one-third of tlie shell from the umbo regularly concentrically 

 corrugated with narrow ridges, and broader and shallow inter- 

 spaces ; the remainder of the shell is usually devoid of regular 

 corrugations, but frequently shows irregular concentric undula- 

 tions. Hinge very thick and solid, and with teeth strongly 

 ■developed. Inner margin of the valves smooth and bevelled off 

 to a sharp edge. Internally the shell is relatively shallow and 

 ■of small capacity. 



Dimensions. — Type specimen, antero-posterior diameter, 69 

 mm.; umbo-ventral diameter, 54 mm.; thickness through both 

 valves, 36 mm.; the slight variation from this may be indicated 

 by the following specimens — 67 mm. by 53 mm., and 66 mm. by 

 53 mm. 



Locality. — Jimmy's Point, Kalimna, Gippsland Lakes. Kalim- 

 nan, — Miocene. 



Oltservations. — This is a fairly common and well-preserved 

 species from the above locality, and at once recalls the living C. 

 kingicola, Lamarck ; it may, however, be distinguished by its 

 greater inflation, its marked posterior attenuation, its shorter 

 .anterior, its umbos much nearer the anterior, and the closer and 

 more numerous umbonal corrugations. Compared with C. 



