THE CAINOZOIC CIDARIDAE OF AUSTRALIA. 
Holotype (test from Morgan, S.A., with spines still attached). Test small 
and low in proportion to width. Ambulacra very slightly wavy. Ambulacral 
plates level, with two vertical rows of small miliary tubercles which consist of 
boss and mamelon ; on each plate the tubercle nearest poriferous zone is the 
larger ; the smaller tubercle placed at 45 degrees downwards from the larger ; 
median suture visible ; margin of plate slopes slightly downwards towards 
suture. Poriferous zones sunken. Pores non-conjugate, circular, close 
together, adjoining pairs separated by a pronounced ridge. Six ambulacral 
plates adjacent to largest interambulacral plate. Interambulacra rather 
broad. Seven coronal plates ; scrobicules sunken, elliptical, becoming circular 
near apex ; boss conical, uncrenulated ; mamelon perforate, contracted at 
base. Plates against apex not divided from adjacent plates below by wide 
horizontal sutures or grooves. Marginal area of plates nearest poriferous 
zones covered with miliaries varying in size and irregularly arranged ; portion 
sloping down to median interambulacral suture covered with scattered miliaries 
which diminish regularly in size towards suture. Suture a slightly zigzag 
line. Tubercles around scrobicule not noticeably arranged into a ring, but 
margin overhangs scrobicule. Scrobicules not confluent ; separated only by 
thin margin in actinal region. Median area of interambulacra broad. 
Spines still attached to test slender, with basal ring finely ridged ; shaft 
slender, cylindrical, tapering towards apex ; surface ornamented with promi- 
nent, upwardly directed spinules, often arranged in longitudinal lines but in 
some instances irregularly scattered ; in one example tip distinctly flared into 
cup-shaped ending. 
Measurements. — Holotype ; diameter of peristome, about 12 mm. ; diameter 
of test, 29 nun. ; height of test, 16 mm. ; width of interamb zone, 15 mm. ; 
width of amb, 4.5 mm. ; width of coronal plate at ambitus, 8 mm. ; height 
of plate, 4.5 mm. Attached spines : length, 21 mm. ; thickest part of shaft, 
2 mm. ; diameter of flared tip, 4.5 mm. 
Observations. — This species lacks some characters of the 
recent genus Gomocidaris and may eventually be separated 
from it. The median suture of the interambulacra, although 
occupying a depressed area, is not bare and shows no sign of 
pits. In the ambulacra there are no bare areas between the 
two rows of miliaries on either side of the suture. 
Crenulated bosses, though absent from the holotype, are 
occasionally present on other specimens. For instance, under 
the microscope one interambulacral zone shows that bosses 
nearest the actinosome are crenulated, and those on a few of 
the many separated plates, probably from near the ambitus, 
are more plainly crenulated ; half the circumference of the 
platform of the boss remains smooth. 
Spines more slender than those of living species, but have characters 
typical of the genus. Chiefly long, slender, delicate with fairly distant, usually 
very sharp, spinules. Shaft rounded to elliptical ; spinules emerge at angles 
ranging from vertical to acute. One variety carries coalescent thorns forming 
a wing on each side of spine ; another clothed closely with short stout thorns ; 
in a third thorns coalesce to form sheath at tip of spine ; one side of shaft 
often bare of spinules ; in others, short spinules are arranged in straight lines 
and they diminish in size towards apex. Surface finely striated in well- 
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