THE CAINOZOIC CIDARIDAE OF AUSTRALIA. 
Cidarid from Aldinga and it is matched with the largest of the 
tuberculated plates of the Aldinga specimens. These latter 
belong to Stereocidaris and indicate a conic test, the broad base 
being nearly fiat, to about one-half the total length of the arc, 
thence roundly bent backward at about sixty degrees ; the basal 
half consists of four plates in each row having areolar areas, the 
posterior ones of which are the largest ; the four or five anterior 
plates in each row are without areoles or one or two may show 
traces of them.” Duncan’s figure of the type specimen (1877, 
pi. Ill, fig. 1) shows both ambulacral and interambulacral 
plates ; we therefore doubt that Tate saw the actual specimen. 
The latter part of the above remarks by Tate concerns a 
fragmentary specimen (an interambulacral zone) in the Tate 
Collection ; this specimen was kindly lent to us for examination 
(PL XII, fig. 3). The ‘‘basal half” is the actinal portion of the 
test, the ‘‘posterior” plates are those near the ambitus and the 
‘‘anterior” plates are those of the abactinal region. With 
regard to the remark by Tate that his specimen indicated a 
conic test, we find that the zone, when placed in a strictly 
vertical position, is not so emphatically indicative of a conic 
test as Tate stated. We think this specimen, which he definitely 
places under 5. australiae, represents a large individual in which 
the upper portion of the test has been crushed. 
A complete test of S. australiae from Aldinga (Tate Collection) bears Tate’s 
ms. name “Goniocidaris inermis,” (PI. XII, figs. 1, 2). The test is both abactin- 
ally and actinally depressed. Each interambulacral zone has feebly scrobi- 
culated plates abactinally, three in left vertical series and two in right. This 
unique specimen also exhibits the only apical system preserved in our fossil 
cidaroids ; all plates are present, even the anal plate, which is depressed into 
the underlying matrix. Measurements: — diameter at ambitus, 34 mm.; 
height of test, 20 mm. ; width of interamb zone at ambitus, 15 mm. ; width 
of amb, 3.5 mm. ; diameter of apical system, 13 mm. ; diameter of peristome, 
10.5 mm. ; width of coronal plate at ambitus, 9 mm. 
Two fragments of tests collected by the late Dr. T. S. Hall from the type 
locality are here figured (PI. XII, figs. 5, 6b). One has six coronal plates in 
vertical series. Abactinal interambulacral plates have a small, shallow 
scrobicule with a rudimentary boss, in striking contrast to the large, deeply 
sunken scrobicules with perforate mamelons nearer the ambitus. Measure- 
ments : — abactinal portion of interamb zone ; height of test, about 19 mm. ; 
greatest width of interamb area, 18.5 mm. ; horizontal diameter of coronal 
plate at ambitus, 10 mm. 
No previous workers have described spines of this species. 
The collections under examination comprise over three thousand 
Australian Cainozoic cidaroid spines, the largest number brought 
together at one time. From these we have selected, on mor- 
phological grounds (as well as because their range and distribu- 
tion are co-extensive with tests of this species), a number which 
we believe to belong to the above species. Some spines of 
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