Older Tertiary of Victoria. 89 



Veiiti'al side flattened, and nearly straight, making an abrupt 

 ascent to the unibonal keel. Umbo to posterior convex, becom- 

 ing flattened towards the posterior margin, the depression being 

 so marked towards the dorsal margin as to appear slightly 

 concave. Dorsal margin straight, and making an angle of about 

 100 degrees with the slightly concave posterior, thence angled 

 again, and nearly straight to join the ventral margin. Surface 

 posterior to the umbonal keel sculptured by strong broad 

 dichotomising ribs, numbering about eight at the umbo, and 

 increasing to twelve or fourteen at the margin ; on the flattened 

 area below the keel the ribbing is of a much tiner and more 

 regular character, there being about twelve flat ribs, with much 

 narrower interspaces on the hinder half of this area, while the 

 forward half is still flner in its ribbing, and the ribs are more 

 arched towards the umbo, instead of running up briefly to the 

 keel. The shell also shows strong irregular concentric growth 

 stoppages, which are inclined to frill the ribs at their intersection, 

 finer concentric lines of growth are also present. Left valve 

 furnished with a relatively strong tooth just below the beak, and 

 a strong pad within for the anterior adductor. 



Dimensions. — Type, length 19 mm.; extreme breadth, 12 mm.; 

 breadth at posterior end, 7 mm.; others have a length of 14 mm. 

 by a breadth of 7 mm., and some have length 12 mm. by breadth 

 7 nnu. 



Localities. — Lower beds of the Spring Creek series, or Bird 

 Rock Bluff", near Geelong. Lower limestone beds of the Maude 

 section, Moorabool Valley. Jan Jukian, — Eocene. 



Observations. — This species at once recalls our living species 

 M. menkeanus, Philippi, but is a much smaller and less solid 

 species, with a more marked keel, and characteristic post-dorsal 

 depression, different outline, and a more twisted umbo. It is 

 equally distinct from the Miocene species, M. submenkeanus, 

 Tate, from Hallett's Cove. 



Glycimepis halli, sp. nov. (PI. XIA"., Figs. 10, 11, 12; 

 PI. XV., Figs. 1, 2, 8, 9). 



Description. — Shell orbicular, tumid, thick and strong, 

 vequilateral, with a prominent convex umbo, and closely radially 



lA 



