Cairns—New flabellid genus from Australian Cenozoic
Description.—The species is known from only one specimen, the holotype. It is essentially conical (Fig. 2.13, 2.14): 17.8mm tall (as measured from the figure) and 10.4 × 10.2mm (as measured from the figure) in calicular diameter (GCD: LCD = 1.02, essentially circular). The angle of thecal diver- gence is uniformly about 27º. The epitheca is porcellaneous. The septa are arranged in four complete cycles: S1–2>S3>S4 (48 septa). The S1–2 are slightly exsert, whereas the S3 are about three-fourths the width of the S1–2, and the S4 are about half the width of the S3. The fossa is deep, containing a some- what unusual (?aberrant) double-lamellar columella (Fig. 2.15).
Remarks.—Periplacotrochus pueblensis is distinctive in having a circular calice and 48 septa, although it is very similar to P. inflectus, as described in the account of that species (see also Key to species in Table 2).
Periplacotrochus inflectus (Dennant, 1903) new combination Figure 3.1–3.4
1903 Placotrochus inflectus Dennant, p. 213, pl. 2, fig. 2a–c. 1981 Placotrochus inflectus; Bell, p. 11 (type deposition). 1989b Placotrochus inflatus (sic); Cairns, p. 75.
Types.—Four syntypes are deposited at the NMV (P27107 and 27108), see Bell (1981). Two additional specimens (?syntypes) are also deposited at that museum: P134078 and P146120. Type locality: “Eocene clays at Brown’s Creek, Aire R. district” (Dennant, 1903, p. 213), Victoria, middle to late Eocene.
Diagnosis.—Corallum with four cycles of hexamerally arran- ged septa but lacking eight S4, resulting in 40 septa; corallum straight to irregularly bent (but not cornute); calice round in cross section.
Occurrence.—Known only from the type locality.
Description.—The species is known from only four specimens, two of them poorly preserved. The specimen described and illustrated by Dennant (1903) is ceratoid (almost conical, Fig. 3.1, 3.2), 7.5 × 6.5mm in calicular diameter (GCD:LCD = 1.15), and 16mmin height (H:GCD = 2.13). The edge angle is about 23º. The epitheca is porcellaneous and the C1–2 are slightly raised. The pedicel attachment is elongate, as is typical for the genus. The septa are arranged in four cycles (S1– 2>S3>S4), but the fourth cycle is incomplete, lacking four pairs of S4 in the lateral half systems, thus resulting in only 40 septa. The S1–2 are thick, their axial edges fused to the colu- mella. The S3 and S4 are much thinner, the S3 about three- fourths the width of the S1–2, and the S4 small. The lamellar columella is prominent (Fig. 3.3, 3.4).
Remarks.—Periplacotrochus inflectus is very similar to P. pueblensis and may simply represent an earlier ontogenetic stage in which the corallum is slightly smaller and thus has an incompletely developed fourth cycle of septa. Most other char- acters are similar or the same. However, the stratigraphic occurrence of P. inflectus is much earlier (middle to late Eocene)
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than that of P. pueblensis (late Oligocene). Clearly, more specimens are needed to resolve this distinction.
Periplacotrochus cudmorei new species Fig. 3.5–3.8
Types.—Holotype: Clifton Bank, Muddy Creek, Victoria, Balcombian (middle Miocene), USNM 1283876. Paratypes: same locality as holotype, two, USNM 1283875. Bird Rock Cliffs, Torquay, Victoria, Janjukian (late Oligocene), four, USNM M353583. Spring Creek, Torquay, Victoria, Janjukian (late Oligocene), three, USNM1283874. Type locality: Clifton Bank, Muddy Creek, Victoria, Balcombian (middle Miocene).
Diagnosis.—Septa arranged in three size classes, having 20 primary septa and thus 80 septa.
Occurrence.—Balcombian (middle Miocene): Muddy Creek, Victoria. Janjukian (late Oligocene): near Torquay, Victoria.
Description.—The corallum is triangular in lateral view (Fig. 3.5), the thecal edges forming an angle of 38º–62º and the planar faces forming a lesser angle of 30º–38º (Fig. 3.6). The lower thecal edges are acute and bear low crests, whereas the upper thecal edges are rounded. The holotype measures 18.2 × 11.7mm in calicular diameter and is 20.0mm in height. The GCD:LCD ranges from 1.42 to 1.68, and the H:GCD ranges from 0.8 to 1.1 but is usually over 1.0. The greater axis of the elongate (1.6–1.9 x 0.7–1.1mmin diameter) pedicel attachment is aligned with the GCD. The 20 costae on the thecal faces are sometimes slightly elevated. The septa are consistently arranged in three size classes:
20:20:40, resulting in 80 septa. The primaries are exsert as much as 1.5mm and have moderately sinuous axial edges, their lower axial edges fusing to the lamellar columella. The secondary septa are about two-thirds the width of the primaries, have less sinuous axial edges, and do not reach the columella. The tertiaries are rather small. The fossa is shallow and contains a prominent lamellar columella (Fig. 3.7, 3.8).
Etymology.—Named in honor of Francis Alexander Cudmore (1892–1956), enthusiastic marine paleontologist who collected in Victoria and Tasmania and provided most of the Australian Tertiary corals donated to the Smithsonian in 1923.
Remarks.—This species is unique in having decameral septal symmetry (see Key in Table 2).
Periplacotrochus magnus (Dennant, 1904) new combination Figure 3.9–3.16
1904 Placotrochus magnus Dennant, p. 54, pl. 22, fig. 4a–c. 1981 Placotrochus magnus; Bell, p. 11 (type deposition). 1989b Placotrochus magnus; Cairns, p. 75 (mentioned).
Types.—The holotype (P27114) and paratype (P27115) are deposited at the NMV. Type locality: Spring Creek (16 miles south of Geelong), Victoria, Australia, Janjukian (late Oligocene).
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