390 
S.D. Cairns 
half of corallum bears a unilinear row of shallow 
circular to slightly elliptical pits, each about 50 pm 
in diameter. In upper half of corallum, pits 
arranged in 2 staggered rows, separated by a thecal 
midline (Figure 6d). Septa hexamerally arranged in 
3 complete cycles (S1>S2>S3). SI about 0.22 mm 
exsert, having straight axial edges that extend 
about half distance to columella in upper fossa but 
join to the columella lower in fossa. S2 equally 
exsert and about 3/4 width of the SI, each bearing 
a broad, low paliform lobe the inner edge of which 
fuses to the columella. S3 relatively narrow (about 
0.1 mm wide), the upper edges of each pair that 
flank an S2 fusing to the S2 at calicular edge 
(forming small lancets) and axial edges of each S3 
angled toward and fusing to its adjacent S2 via 2 
or 3 trabecular processes. Fossa of moderate depth; 
columella a solid central fusion of inner edges of 
SI and P2. 
Remarks 
Conocyathus gracilis is similar to and has been 
confused with C. zelandiae, but is distinguished by 
having a smaller, narrower corallum (GCD max. 
1.7 mm and H:D = 3.1 vs GCD max. 3.4 mm and 
H:D = 1.8); having much less exsert P2 (those of C. 
zelandiae extend above the calicular edge); having 
only 24 costae, the C4 of C. zelandiae beginning to 
form at a height of 1.9-2.7 mm; having broader 
intercostal region than costae, the reverse being 
true for C. zelandiae; and in having uniformly wide 
Cl-2 that do not change width at the origin of the 
C3. 
Distribution 
Western Australia: known only from continental 
shelf of northwestern coast off Broome and Glomar 
Shoal; 101 m. Elsewhere: Arafura Sea (off Arnhem 
Land, Northern Territory); 22-291 m. 
Etymology 
The species name gracilis (Latin gracilis, slender) 
alludes to the slender corallum of this species, 
which helps to distinguish it from C. zelandiae. 
Genus Alatotrochus Cairns, 1994 
Alatotrochus rubescens (Moseley, 1876) 
Platytrochus rubescens Moseley, 1876: 553. 
Sphenotrochus rubescens - Moseley, 1881: 157-159, 
pi. 6, figs 8, 8a. 
Alatotrochus rubescens - Cairns, 1994: 68-69, pi. 29, 
figs g-1 (synonymy); 1995: 84, pi. 24, figs. a-b.— 
Cairns and Zibrowius, 1997: 141-142, fig. 18 h. 
New Records 
Lady : stn RW96-17, 3: 2 (NTM C8069 and C8074), 
1 (USNM 98515); stn RW96-18, 1 (NTM); stn 
RW96-19, 1 (NTM C8084). 
Distribution 
Western Australia: south of Cartier Island; 180- 
350 m. Elsewhere: western Pacific from Japan to 
southern Norfolk Ridge; 187-751 m (Cairns and 
Zibrowius 1997). 
Genus Idiotrochus Wells, 1935 
Idiotrochus kikutii (Yabe and Eguchi, 1941) 
Placotrochides kikutii Yabe and Eguchi, 1941: 104. 
Idiotrochus kikutii - Cairns, 1989: 36-37, pi. 18, figs, 
a-b, d-h (synonymy and description); 1994: 69, 
pi. 30, figs. a-d.—Cairns and Zibrowius, 1997: 
148-149. 
New Record 
Soela: stn 02/82/13A, 3, WAM 90- and 96-84. 
Distribution 
Western Australia: continental slope of 
northwestern coast off Port Hedland; 201 m. 
Elsewhere: western Pacific from Japan through 
Indonesia; 97-645 m (Cairns and Zibrowius 1997). 
Genus Notocyathus Tenison Woods, 1880 
Notocyathus venustus (Alcock, 1902b) 
Citharocyathus venustus Alcock, 1902b: 119. 
Notocyathus venustus - Cairns, 1989: 27-28, pi. 12, figs, 
c-h (synonymy and description); 1994: 64, pi. 27, 
figs. k-L—Cairns and Zibrowius, 1997: 143. 
New Records 
Soela: stn 01/79/unnumbered, 2, WAM 32-85. 
Umataka Marti: stn 6921, 10: 7 (WAM 150-84 and 
325-89), 3 (USNM 97010); stn 6927, 1, WAM 103-84. 
MV Kos 2: stn K67-182, 14°12'S, 123°02’E, 194 m, 
1, AMS G15353. 
Lady: stn RW96-17, 1, NTM C8072. 
Distribution 
Western Australia: northwestern coast from 
Cartier Island to off Glomar Shoal; 90-300 m. 
Elsewhere: western Pacific from southern Japan 
through Indonesia; 70-555 m (Cairns and 
Zibrowius 1997). 
Genus Tropidocyathus Milne Edwards and 
Haime, 1848a 
Tropidocyathus lessottii (Michelin, 1842) 
Flabelluttt Lessonii Michelin, 1842: 119. 
Tropidocyathus lessottii - Cairns, 1989: 33-34, pi. 16, 
figs, d-1 (synonymy and description); 1994: 67, 
