THE CAINOZOIC CIDARIDAE OF AUSTRALIA. 
middle of this area only slightly zigzag. Horizontal sutures between coronal 
plates end against poriferous zone in small well-defined pits, but in median 
interambulacral area they terminate in deep, v-shaped grooves or pits. Half- 
way between any two of these latter grooves, opposite centre of each plate, 
is a much smaller depression in sunken median area. 
Spines short, probably never as long as horizontal diameter of test. Many 
retain original purplish colour. Ring milled, collar finely striated. No 
narrowing of shaft near neck ; it sometimes thickens slightly above neck, then 
tapers to apex ; tapering often very slight. Spines covered with short thorns, 
irregularly arranged, inclined a little towards apex. A few spines flattened 
apically. Apex more or less flared, often cup-shaped ; diameter of cups never 
exceeds that of thickest part of shaft. 
Measurements .- Holotype (test fragment) : vertical length of four coronal 
plates, 19.5 mm. ; height of largest plate, 5.25 mm. ; width of largest plate, 
9.5 mm. ; width of amb plate, ,3.5 mm. Paratypes (spines) : length of longest 
spine, 23 mm. ; diameter of shaft, 2.5 mm. 
Observations. — Goniocidaris mortenseni is very close to the 
living G. tubaria, but has a less depressed test, fewer tubercles 
on the portion of the coronal plate next the interambulacral 
zone, and broader and shorter v-shaped grooves. The inter- 
poriferous area as far as the suture, not counting marginal 
tubercles, is more sunken, and is equal in width to the poriferous 
zone. The poriferous zone is more sunken, and the longitudinal 
ridge of tubercles marginal to it is far more pronounced. Only 
fragments of the test have been found. Spines and test- 
fragments are from the same stratum and are undoubtedly 
conspecific. The spines differ from those of living species in 
being more slender and rarely flattened ; they terminate in 
tiny cup-shaped flares, whereas the apex in recent spines is 
shaped like a nearly fully opened hand. 
We have named this species after Dr. Th. Mortensen, whose 
magnificent Monograph on the Cidaroida has proved of the 
greatest help to us. 
Localities. — South Australia — Aldinga, upper beds (holotype, C. ; para- 
types, 6 spines from same beds, C ; also “C.”) 
Range. — Lower Pliocene. 
Genus CHONDROCIDARIS A. Agassiz 1863. 
Both living species of Chondrocidaris are confined to the 
Indo-Pacific. A possible fossil form of this genus occurs in 
the (?) Miocene of Madagascar. Some of the spines described 
as Phyllacanthus sundaica Martin from the Miocene of Java 
probably belong to the same genus. The pores are conjugate 
(Mortensen, 1928). 
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