Tertiary.) PALAEONTOLOGY OF VICTORIA. (Mollusca, 
The depth and thickness increase greatly with age, the form 
becomes more elongated in the direction of the depth from the 
beak to opposite margin, slightly angulated on the posterior side ; 
the ribs become less prominent and ultimately almost obsolete at 
the margin, the cardinal ligamental area increases, and the teeth 
diminish in number from the middle ones becoming obsolete. In 
all respects, and in the variations, there is the most complete identity 
between our fossil and the living species to which I have no hesi- 
tation whatever in referring it; although it must be a matter of 
astonishment to find that one of the few living species of shells 
in our Oligocene and Lower Miocene Tertiary beds should be an 
inhabitant, not of our seas, but of the North-Eastern portion of 
New Zealand and the Chatham Islands, between which coasts and 
the Victorian there are scarcely any recent mollusca in common, 
and between us being water of the deepest soundings. 
This species occurs of large size, often with the valves still in 
contact, showing they have not been moved from the spot on which 
they lived, and in the utmost profusion, in the Tertiary sands and 
muds of the cliffs at Bird Rock, Geelong. Nearly as abundant, but 
smaller, in the clays between Mount Eliza and Mount Martha, at 
Schnapper Point. 
EXPLANATION OF FIGURES. 
Plate XTX.—Fig. 10, interior of moderate sized specimen, natural size. Fig. 10a, profile 
showing depth or convexity of valve. Fig. 11, exterior view, natural size, of moderately grown 
specimen, showing the angulated character of ribs and distinct interspaces. Fig. 12, interior of 
young specimen, natural size. Fig. 13, still younger specimen, outer surface, natural size. 
Fig. 14 (9 by error on plate), adult, natural size, showing obtuse nearly obsolete character of ribs 
towards margin, with comparatively narrow interspaces, 
Freperick McCoy. 
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