Older Tertiary of Victoria. 29 



deeply excavated lunule. Umbo convexly rounded, and running 

 out to an acute point just above the cardinal area. Outline of 

 the shell very regularly rounded, but for the slight interruption 

 in the neighbourhood of the lunule. Inner margin crenulated 

 from the lower margin of the lunule to the posterior end of the 

 hinge in accordance with the external radial ridges. External 

 surface sculptured with fine close radial ridges, the interspaces 

 being narrower than the ridges, but widest on the posterior 

 slope, and widening towards the margin ; ridges number about 

 28 to 30, and are very regularly and finely beaded, the beads 

 being more rounded in the neighborhood of the umbo, then 

 becoming more oval, and then more oblong towards the ventral 

 margin. Interspaces apparently smooth, but under a good lens 

 show fine concentric markings. 



Dimensions. — Antero-posterior diameter, 5 mm.; umbo-ventral 

 diameter, 5 mm.; thickness through one valve, about 2 nmi. 



Localities. — Type from the Eocene clays of Grice's Creek ; also 

 from the clays near the Old Cement Works, Balcombe's Bay, 

 Mornington. 



Observations. — The present form appears entirely distinct from 

 any of the five species of this genus already described by 

 Professor Tate, and may be said at first sight to somewhat recall 

 Cardita delicatula, Tate, but its hinge characters are exactly 

 those of Carditella, and at the same time it is smaller on the 

 average, more rotund, more convex, and with finer sculpture, 

 than that species. 



Modiolaria balcombei, sp. nov. (PL III., Fig. 2). 



Description. — Shell small, oblong-oval, very tumid, especially 

 at the umbo and about the umbonal ridge, maximum convexity 

 about the median portion of the shell, thin and nacreous 

 internally. 



Umbo very prominent, strongly incurved, and terminal ; 

 anterior margin only slightly convex to the ventral margin ; the 

 latter showing a distinct sinus, dorsally the margin is convexly 

 rounded, inclined to angulation with the posterior margin, on 

 account of oblique truncation, and again, slightly angled where 

 the umbonal ridge runs out. The whole of the inner margin 



