Older Tertiary of Victoria. 27 



but showing both valves in contact, and sufficiently well preserved 

 to give the following : Antero-posterior diameter, 37 mm.; 

 greatest breadth, 18 mm.; greatest thickness through both 

 valves, 16 mm. 



Locality. — Eocene, lower beds of the Spring Creek or Bird 

 Rock Bluff", near Geeloiig. 



Obsefvations. — Apparently closely related to M. adelaidensis, 

 Tate, from the Adelaide bore, but differs in relative dimensions, 

 and amongst other features the presence of the ventral sinus, 

 and surface sculpturing serve as features of distinction. 



Leda acuticauda, sp. nov. (PL III., Figs. 4, 4a). 



Description. — Shell small, ovate-subtrigonal, anterior end 

 convexly rounded and shorter than the posterior, the latter being 

 drawn out into a very acutely pointed end. 



Umbo prominent and inflated, apparently smooth, and directed 

 slightly towards the posterior, in paired valves the umbones are 

 in contact. The anterior hinge makes, with the posterior hinge, 

 an angle of about 104°, each carrying about twelve to fourteen 

 angular teeth. The posterior hinge line is rather i-emarkably 

 straight or very .slightly concave, while the anterior is slightly 

 convex. Behind the hinge on the posterior slope from the umbo 

 the valve is characteristically flattened, causing a marked 

 posterior keel. Internally the ventral margin is broadly bevelled. 

 The angulation made by the posterior margin with the ventral 

 margin is about 50", but the junction is so pointed as to nppear 

 more acute. Externally the valves are very flnely concentrically 

 striate, and usually show irregular growth foMs. 



JDiinensio?!s. — Type specimen, antero-posterior diameter, 7 mm.; 

 umbo ventral diameter, 4 mm.; thickness through both valves, 3 

 mm.; other specimens range from this to 6 mm. l>y 4 mm. down 

 to small young examples which measure 3 mm. by 2 mm. 



Localities. — Eocene clays of Grice's Creek, and from the clays 

 near the old Cement Works, Balcombe's Bay, Mornington. 



Ohservatio7is. — This species might at first sight be mistiken for 

 L. apiculata, Tate, but upon examination many points of 

 distinction can be readily made out. The present species has a 

 different hinge angulation, a more marked posterior keel, and 



