Tertiary.) PALZONTOLOGY OF VICTORIA. [Mollusea. 
ones, many specimens of which are perfectly identical in all other 
respects. Some specimens are less oblique, and many specimens 
are more convex than the typical ones, which agree precisely with 
the recent shell in these respects. 
Very abundant in the Oligocene Tertiary clays of between Mount 
Martha and Mount Eliza, in Hobson’s Bay. Very common in similar 
clays of Muddy Creek. Abundant in a whitish clay at Moorabbin. 
Abundant in fine sandy beds at Corio Bay (A* 15); in similar 
beds (A¥), 3 miles W. of mouth of Gellibrand River. 
EXPLANATION OF FIGURES. 
Plate XTX.—Fig. 8, specimen of ordinary character, outer surface, natural size. Fig. 8a, 
portion of surface of ditto magnified. Fig. 9, inside view of another specimen, natural size. 
Puate XIX., Fras. 10-14. 
PECTUNCULUS LATICOSTATUS (Quoy anp Garmarp). 
[Genus PECTUNCULUS (Lam.). Sub-kingd. Mollusca. Class Dithyra. Order Pecti- 
nacea. Fam. Arcide.) 
Gen. Char.—Shell suborbicular ; beaks small, nearly central; equivalve, nearly equilateral, 
closed all round ; substance very thick ; hinge-teeth forming a curved line of very numerous 
teeth, small and transverse under the beak, larger and oblique at the ends, more numerous on 
the posterior than on the anterior side; ligament and cartilage on V-shaped lines diverging 
from beneath the beaks, on a flat triangular cardinal area in each valve. | 
DescrrptTion.—Orbicular when young, slightly subtrigonal, and the length from 
anterior to posterior side rather greater than the depth from beak to opposite margin ; 
with age becoming ovate, and depth from beak to ventral margin the greatest 
measure. Surface regularly radiated with about 39 ribs from the beak, subangular, 
sharply defined, and separated by transversely striated channels in the young ; becoming 
gradually broader, less convex, and only separated by narrow impressed lines towards 
the margin in old specimens; whole surface with close, sharp, concentric strie of 
growth; inside of margin strongly denticulated; hinge-teeth vary from 5 to 14 on 
each side (usually 2 more on posterior than on the anterior side of the beak); 
cardinal area small in the young, forming very large flat triangular area with very 
numerous close V-shaped ligamental striz in the old. Old, depth about 3 inches 
from beak to ventral margin; proportional to this the greatest leneth from anterior 
to posterior side is 7%", ; depth of one valve, =34;. Young, length from anterior to 
posterior edge, 6 lines; proportional to this greatest measurement, depth from beak 
to ventral edge, °5,; thickness of one valve, =°,. At 3lines from the beak there 
are about 10 ribs in 2 lines; but at 3 inches from the beak 2 ribs occupy 4 lines. 
REFERENCE. —P. laticostatus + P. ovatus (Quoy and Gaimard), Voy. de 
V Astrolabe, t. 77, figs. 1 to 6. 
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