THE CAINOZOIC CIDARIDAE OF AUSTRALIA. 
wards. The large upper tubercles have a smaller scrobicular area than those 
in the middle of the test ; and the tubercles diminish rapidly in size towards 
the actinosome.” 
Observations . — Duncan stated that the pores are conjugate, 
but all our specimens of this species from the type locality 
(Castle Cove, near Cape Otway) and from Aldinga (Port 
Willunga) have non-conjugate pores, a character seen in 
Stereocidaris. The pores of a pair are close together, the inner 
round and the outer slightly oblique. 
The poriferous zone is narrow. Adult specimens have 
12 ambulacral plates adjacent to the largest interambulacral 
plate at the ambitus. The larger ambulacral plates bear 
numerous tubercles and granules, comprising several vertical 
rows. The test is small to medium. As in recent species, the 
non-spine-bearing abactinal coronal plates vary considerably in 
number in different tests ; several of the uppermost plates often 
have a shallow scrobicular area, tiny in proportion to the size 
of the plate, with a small imperforate boss. We have found no 
trace of crenulation in adult specimens, but one young test 
from Aldinga (“C”)* shows partial crenulation of the primary 
tubercles. Interambulacra are narrow. Scrobicules are circular, 
except below the ambitus, where they are slightly elliptical. 
Tubercles composing the ring round the scrobicules are small 
and the ring is inconspicuous. Scrobicules are not confluent, 
though in the actinal region the rings merge together. They are 
often far more sunken than in any other Australian Cainozoic 
cidaroid, but this character is variable. 
The median area of the interambulacrum is very narrow in 
young specimens, widening with age ; in the actinal region, 
especially in young specimens, it is very little sunken, but pits 
usually occur at the ends of horizontal sutures between coronal 
plates. The ends of sutures nearest the ambulacra sometimes 
form slight grooves. There are commonly six or seven coronal 
plates in a vertical series ; some specimens from Aldinga with 
six vertical rows of tubercles in the interporiferous area have 
up to nine plates. The deeply sunken scrobicules and, as a 
rule, lack of perforate mamelons on the abactinal plates, readily 
distinguish this species from others included in this paper. 
During the last fifty years there has been much confusion in 
regard to this variable cidaroid. The holotype, which came 
from Castle Cove (Aire Coast, Wilkinson’s No. 5 Section) is in 
London, and we have not seen it. Tate (1898, p. 411) states 
that he had compared Duncan’s type, “which is a single inter- 
ambulacral plate, with complete interambulacral zones of a 
*For abbreviations see p. 142. 
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