bullarensis sp. nov.
Plate 90, figs. 3, 4 ;
Plate 91, figs. 1-3
occurrence. Twenty-three specimens from the northern en of Giralia
Anticlin, Carnarvon Basin on Giralia Station, North West Division,
Western Australia. Nine, including the holotype (WAM 73.361) and two
paratypes (WAM 73.365, 73.366) are from the south side of the Bullara-Giralia
road in the vicinity of the turn-off to Jubilee Bore at approximatly
22° 40' S., 114°, 13' E., and about 6.5 km south of the bore. Although
the echinoids were not found in situ they have traces of white
glauconitic lime mudstone adhering to them. Eleven reddish silicified
specimens were found loose 400 m south of a white hill about 5 km
south of Jubilee Bore at approximately 22° 39' S., 114° 14' E. NMV
P31199 was collected by T. A. Darragh and labelled 'Wadera Calcarenite,
float on E. side of Main N.-S. tract of C-Y Creek (due E. of bore and
E. of fence, Open Country Paddock), Yanrey 188147', at approximately
22° 52' S., 114° 7' E. A further two crushed echinoids( P31227, 31228)
are probably the same species. They are from the type section of the
Wadera Calcarenite, Old Marilla Station at 22° 50' S., 114° 8' E.
The dimensions of the holotype are : length 20 mm, width 17 mm, height
10 mm. Other specimens from the same locality range from 14 x 11 x8 mm
up to 25 x 21 x 11 mm.
Adapical and adoral surfaces flattened, with the ambitus uniformly
rounded. Prominent plastronal keel which terminates in a slight anal
rostrum ; anterior margin gently rounded at the ambitus.
Apical system in front of centre, disjunct, with three genital pores ;
that of the madreporiste is lacking. Ambulacra composed of small
pore-pairs not easily discernible in unweathered specimens. Adapically
the small round pores are placed close together and separated by a
granule. The pore-pairs in the paired ambulacra placed slightly
en-chevron ; in ambulacrum III they are almost longitudinally directed.
Transversely oval periproct located just above anal rostrum.
Subcircular, anteriorly located peristome with prominent phyllodes
composed of deeptly countersunk pores. Test coated with coarse
granules and relatively dense small primary tubercles. Adoral surface
with dense plastronal tuberculation but tubercles absent in the
phyllodes and ambulacra I and V.
Plastronal plating consisting of a relatively long labrum extending to
the second ambulacral plate followed by a single large sternal plate
extending to the fourth ambulacral plate. There follows a pair of
episternal plates (the suture which separates them is only discernible
with difficulty in the available material). The episternals are
succeeded by a single plate, in the position of the point of the
rostrum, and then two pairs of pre-anals. A subcircular subanal
fasciole encloses the rostral plate.
This new species is readily distinguished from specimens of
Corystus dysasteroides in the Australian Tertiary by its smaller
size, three genital pores, flat upper and lower surfaces, less
prominent pore-pairs arranged en-chevron, subcircular peristome,
coarser and more dense tuberculation, and the absenc of a frontal