THE CAINOZOIC CIDARIDAE OF AUSTRALIA. 
recent species of the genus figured by Mortensen (1928, Plates 
XIX and XXII) are almost identical in appearance with certain 
of the fossil spines. Our specimens may be divided into several 
minor groups, which, however, shade into one another. 
One variety from the lower beds at Aldinga, from Castle Cove and from 
Point Flinders near Cape Otway, is long, comparatively slender, and circular 
in section ; in some cases it is almost twice the horizontal diameter of the test 
in length. Length of longest spine, apex missing, from Aldinga, about 85 mm. ; 
a similar spine from near Cape Otway, apex missing, 63 mm. Shaft, which in 
the longer specimens flattens slightly towards apex, ornamented with closely 
set ridges bearing short spinose tubercles ; these tuberculate ridges usually 
extend close to apex, in which case the spine is generally slender and has an 
almost terete habit, but close to apex it broadens and terminates in a cup- 
shaped structure on exterior of which the vertical ridges become coarser and 
more salient. Interior of cup smooth or slightly radiately granulose. Between 
ridges, surface of shaft is very finely longitudinally striated ; the striae continue 
across neck, collar and ring. 
A second variety is found at Castle Cove and in lower beds at Aldinga ; 
spines long, slender, with tuberculate or bluntly spinose ridges similar to those 
already mentioned and two coarser spinose ridges upon opposite sides of 
shaft ; in some the spinules coalesce to form an alate ridge. Terminations 
less cupped, palmate. Portion of shaft next apex flattened and sometimes 
curved. Both in character of spinose side ridges and of palmate termination, 
the second variety differs from spines of living forms and is more like certain 
spines of Goniocidaris and Prionocidaris ; but after examining a long series, 
we are satisfied that they belong to Stereocidaris anstraliae, as do the allied 
spines more typical of the genus. Their occurrence in a fossil species supports 
Mortensen’s suggestion (1928, p. 230) that the Goniocidarids may have been 
derived from the Stereocidaris- like forms. 
A link between the two groups of spines is provided by a third variety 
from near Cape Otway and from lower beds, Aldinga : more generally spinose 
and with palmate ending. 
All these varieties have excessively fine vertical striae on surface of neck, 
collar and ring. Crenulation of outside of margin of acetabulum is rarely 
preserved. 
A fourth variety tapers, and has prominent wing-like projections on either 
side near base (see Clark, 1925, p. 26). Near Cape Otway and at Aldinga 
(Tate and “C.” Colls.) spines of this species are common ; at Aldinga some 
have narrow encircling colour bands (“C.” Coll.). 
Measurements. — Length of complete cup-ended spine from near Cape 
Otway (plesiotype) , 26 mm. ; another spine, apex missing, 58 mm. ; diameter 
of widest cup, 9 mm. ; length of spine (plesiotype) from Aldinga, apex missing, 
86 mm. 
Localities. — Victoria — Castle Cove, Aire Coast, Wilkinson’s No. 5 Section 
(“C.” ; plesiotypes, 3 interamb zones, H., C.). Point Flinders, near Cape 
Otway, Aire Coast No. 1 Section of Geol. Surv. (Plesiotypes, 2 spines and 
4 cupped terminals, C. ; also W. and “C.”). Quarter mile northerly from 
Bird Rock, Torquay, in polyzoal rock (a small test ; “C.”). Mitchell River 
(a test fragment ; D). South Australia — Aldinga, lower beds (Plesiotypes, 
interamb zone, D ; 10 spines, C ; 3 plesiotypes in Tate Coll. ; specimens in 
S., “C.” and Tate Coll.). Wongulla, lower beds (a small test ; “C.”). 
Range. — Upper Oligocene to Miocene. 
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