THE CAINOZOIC CIDARIDAE OF AUSTRALIA. 
The tests are medium to large, tall and a little depressed abactin- 
ally. The poriferous zone is distinctly sunken and pores are 
not close together. Ambulacral plates show two, three, or even 
four vertical rows of tubercles ; a fourth row occurs on a large 
imperfect test from Port Macclonnell which was at first thought 
to represent a distinct species, but its large size appears to be 
merely a feature of senility. At Batesford there occur coronal 
plates (25.5 mm. by 14 mm.) from tests which were even larger. 
Coronal plates in the vertical series are probably seven in 
number. Interambulacral zones from Bairnsdale, whence came 
the original specimen, and from Batesford, show that the median 
area at the ambitus is broad, with plate margins sloping slightly 
down to the suture. The scrobicular rings do not overhang the 
scrobicules ; the latter are nowhere confluent, though the rings 
merge in the actinal region. The area beyond the rings is 
covered with closely-packed miliaries. 
J. W. Gregory (1890, p. 482) has recorded this species from 
Willunga, South Australia, but the fossil probably came from 
Port Willunga on Aldinga Bay. Unless the fragment came from 
the upper bed, it almost certainly represents the new species 
now named Prionocidaris scop aria. 
Neither Duncan nor Tate figured cidaroid spines. Some 
spines from the same stratum as the tests of Phyllacanthus 
duncani are undoubtedly conspecific ; they are all fairly long, 
very gradually tapering, without thorns, somewhat rounded at 
the end, with a moderately blunt point. Minor characters 
divide them into two varieties which we have never found 
together in the same bed. There is no variation in the tests, 
and possibly further collecting may show that differences in the 
spines are due either to their range in time or to factors of 
environment. 
In the first kind, ring is milled by fine lines which cross it vertically ; above 
ring shaft narrows, then widens before tapering towards apex, maximum width 
being sometimes greater than diameter of ring. Shaft covered with fine 
granules, irregularly scattered near neck, but a little above it arranged in 
straight lines, giving blunt apical portion a ridged or fluted appearance. Viewed 
under high magnification, remainder of the surface is a network of fine cells. 
Localities. — Victoria — Mitchell River at Bairnsdale (N.M., “C.” and "G.C.”). 
Swan Reach (“G.C.”). Nicholson River (“C.”). Curlewis, locality Ad 12 or 
13, Geol. Quarter Sheet 23 SW. (N.M.). Beaumaris, washed out into the 
shingle ("C.”). South Australia — Beach at Port Macdonnell (“H.”). Aldinga, 
upper beds (no narrowing or swelling of spines; “C.”). Upper beds near 
Morgan, Murray River (“C.”). 
Spines of second kind have no constriction above collar. Granules coarser, 
linearly arranged nearer neck. The network of cells visible only in exception- 
ally well-preserved specimens. Diameter of shaft rarely as much as that of 
ring ; spine tapers evenly to blunt end. 
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