THE CAINOZOIC CIDARIDAE OF AUSTRALIA. 
Chondrocidaris clarkii sp. nov. 
Plate XIII, figs. 15-17 ; Plate XV, fig. 31. 
Syntype from Morgan : an almost complete young test, actinal portion of 
one interamb zone alone missing ; somewhat flattened at apex, depressed 
abactinally, of medium size. Ambulacra wide, nearly straight ; level inter- 
poriferous areas at ambitus with six vertical rows of small miliary tubercles, 
two of which disappear towards actinosome and probably also towards apex. 
Ao trace of median depression, but suture visible. Poriferous zones slightly 
sunken. Pores conjugate, oval, close together. Ten ambulacral plates 
adjacent to largest coronal plate. Interambulacra broad. About eight 
coronal plates ; marginal area adjacent to poriferous zone flat. Boss uncrenu- 
lated ; small mamelon, contracted at neck. Scrobicules deeply sunken, not 
confluent ; elliptical at ambitus and towards actinosome, circular towards 
apex ; bounded by a ring of tubercles which slightly overhangs margin ; 
tubercles composing ring widely spaced, the space between any two being 
entirely bare and not invaded by granules placed beyond ring. Median area 
of interambulacra broad and flat ; no trace of median depression ; uniformly 
covered with small, closely packed miliaries. Median suture either invisible 
or very faint. 
Syntype from near Overland Corner : a perfect adult test, large. Abactinal 
region well shown. Rows of small miliary tubercles in ambulacra similar to 
those of smaller syntype. Suture a fine line in almost flat median inter- 
ambulacral area. Entire perignathic girdle visible. Eight coronal plates ; 
marginal areas adjacent to poriferous zone almost flat. Fourteen ambulacral 
plates opposite largest coronal plate. 
Measurements. — Syntype from Morgan : diameter across peristome, 13 mml 
horizontal diameter of test, 36 mm. ; height of test, about 22 mm. ; width of 
interamb area at ambitus, 17.5 mm. ; width of amb, 4.25 mm. ; width of coronal 
plate at ambitus, 9.25 mm. ; height of plate, 5.25 mm. Syntype from below 
Overland Corner : horizontal diameter, 62 mm. ; height, 33 mm. ; diameter 
across apical system, about 21.5 mm. ; diameter across peristome, 20.5 mm. ; 
width of interamb area at ambitus, 30 mm. ; width of amb, 6 mm. ; width of 
coronal plate at ambitus, 16 mm. ; height of plate, 9 mm. 
Spines resembling those of living species of Chondrocidaris occur in same 
strata as tests, and evidently belong to this species. Figured paratypes from 
an infilled pocket in strata at Morgan evidently came from one individual. 
Length of longest spine, 50 mm. Long, slender, thorny near base, longitudin- 
ally ridged towards apex. Collar finely striated ; lines crossing ring give it a 
milled appearance. Plane of ring not at right angles to shaft. No narrowing 
of shaft above collar, and little tapering. Near collar, shaft is circular in 
section, but it gradually flattens. More flattened side bare of ornament near 
collar ; for more than half length of shaft bears broad, thin thorns, outwardly 
directed, becoming wing-like along sides of shaft ; these thorns give place to 
thin ridges capped with outwardly directed points. Ridges end at blunted 
spinal apex. A smaller spine (30 mm.) has no ridges, but ends in winged 
apex with serrated edges : an identical spine was collected at Brown’s Creek, 
Cape Otway district. Another spine (16.5 mm.) bears only fine serrated 
ridges which increase in height towards blunt apex. All retain traces of 
original purple colour. 
Observations. — The principal features distinguishing the above 
species are the typically flattened and closely granulated plates 
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