Upper Silurian.} PALZAONTOLOGY OF VICTORIA. [ Mollusca, 
moderate sharp edged. Triangular chamber in beak of receiving valve small, and its 
medial septum extending rather less than half the length of the valve; two septa 
from cardinal teeth of entering valve about one-sixth the length of the shell, slightly 
arched with concavity inwards, enclosing a sub-ovate rostral space, in front of which 
are two slight indications of parallel ridges with a still slighter medial one, not 
reaching the middle of the shell. Casts of receiving valve longitudinally rugoso- 
granulate, with mesial septum about half the length of the shell; cast of entering 
valve with a prominent ovate rostral space defined by the two arched septa or dental 
lamellz, from which a broad flattened prominent nearly parallel-sided projection 
extends nearly to the middle of the shell, pointed towards the beak, and gradually 
blending with the surface of the shell in front, usually showing a faint mesial furrow, 
in the middle of which and on each side three small slits seem to indicate slight 
internal septa rising from inner surface of valve. Length of entering valve, varying 
from 13 to nearly 3 inches; proportional width, about 3°;; depth of entering valve, 
about +5. (Owing to imperfections of specimens the proportional measurements 
cannot be given precisely.) 
This may be looked upon as an Australian representative of the 
European and American P. oblongus of exactly the same geological 
horizon at base of Upper Silurian, which it strongly resembles in 
size, shape, and surface. It is, however, perfectly distinguished by 
the inarching of the septa of the entering valve and the large ovate 
rostral space so defined in the casts. These plates do not converge 
to the middle like those forming the rostral chamber of the 
Bohemian P. Siebert. 
Abundant in the May Hill sandstones (base of Upper Silurian) 
of section 12, parish of Yering. 
EXPLANATION OF FIGURES. 
Plate XLVII.—Fig. 9, internal cast of large specimen of entering valve (imperfect in 
front), showing ovate rostral space, enclosed by inarched dental lamellz, with the pointed 
nearly parallel-sided mesial elevation divided by small median sulcus, natural size. Fig. 9a, 
rostral view of same specimen. Fig. 10, internal cast of beak of receiving valve, showing 
internal lines of granulo-punctate surface with mesial septum and rostral chamber, and a faint 
indication of the cardinal area. Fig. 11, obliquely compressed specimen of entering valve, 
showing the surface with faint radiating irregular markings and lines of growth, together 
with the two inarched rostral plates, and the more anterior pair of slightly indicated parallel 
septa with slighter ridge between them, natural size. Fig. 12, another less distorted specimen 
of same valve, showing the surface, natural size. 
Freperick McCoy. 
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