412


Journal of Paleontology 91(3):407–416


smaller corallum, straight (not convex) thecal faces and thus a less full corallum, consistently 96 hexamerally arranged septa (vs. three size classes of septa, the largest counting 28–32), consistently crested lower thecal edges, and ribbed C1–3.


Periplacotrochus corniculatus (Dennant, 1899) new combination Figure 2.5–2.7


1899 Placotrochus corniculatus Dennant, p. 115, pl. 2, fig. 3a–b.


1927 Placotrochus corniculatus; Felix, p. 416. 1981 Placotrochus corniculatus; Bell, p. 11 (type deposition). 1989b Placotrochus corniculatus; Cairns, p. 75 (mentioned).


Types.—Holotype deposited at the NMV (P27069); paratype NMV P27070 (Blanche Point); Dennant (1899) mentioned a third specimen, which would also be a paratype. Type locality: Adelaide bore, South Australia, Miocene according to Felix (1927).


Diagnosis.—Corallum with four cycles (48 septa) of hexam- erally arranged septa; corallum cornute.


Occurrence.—Known only from the type locality.


Description.—This species is known only from three speci- mens. The holotype is a cornute specimen (Fig. 2.5), curved about 75º. It is 20mm in height and 9.0 × 6.5mm in calicular diameter, having a H:GCD of 2.2. The GCD:LCD range of the type series is 1.21–1.56. The edge angle is about 13º; the face angle could not be computed from the figures or text. The septa are arranged in four complete cycles: S1–2>S3>S4 (48 septa). The S1–2 are slightly exsert with strongly sinuous axial edges. The S3 are almost as wide as the S1–2, and the S4 are relatively small. The fossa contains a typical lamellar columella.


Remarks.—This species is distinguished from the others in the genus by having a regularly curved (cornute) corallum (see Key in Table 2).


Periplacotrochus elongatus (Duncan, 1864) new combination Figure 2.8–2.12


1864 Placotrochus elongatus Duncan, p. 163, 167, pl. 5, fig. 4a–e.


1870 Placotrochus elongatus; Duncan, p. 300, 311, 312, 313, pl. 20, fig. 3a–c.


1878b Placotrochus elongatus; Tenison-Woods, p. 314. 1927 Placotrochus elongatus; Felix, p. 417. 1989b Placotrochus elongatus; Cairns, p. 75.


Types.—The holotype is deposited at the NHMUK (PI R29274). Type locality: Muddy Creek, Victoria (middle Miocene).


Diagnosis.—Corallum with four cycles (48 septa) of hexam- erally arranged septa; corallum straight to irregularly bent (but not cornute); calice elliptical in cross section.


Occurrence.—Janjukian (late Oligocene): Torquay, Victoria. Balcombian (middle Miocene). Muddy Creek, Aire River, Grice’s Creek, Victoria. Miocene: Table Cape, Tasmania, Mount Gambier, Cape Otway, Victoria.


Description.—The corallum is shaped as an isosceles triangle (Fig. 2.9), the edge angle ranging from 17º–29º and the thecal edges being straight. The thecal faces are planar (not convex), having a face angle of 12º–22º (Fig. 2.10). The lower thecal edges are acute but not crested; the upper thecal edges are evenly rounded, producing an elliptical calice having a GCD: LCD of 1.50–1.67. The H:GCD ranges from 1.6 to 3.2, thus the name elongatus. One of the larger coralla (USNM 77069) measures 11.3 × 7.3mm in calicular diameter and 22.3mm in height. The pedicel is small, about 1.9 × 1.0mmin diameter, the longer axis aligned with the GCD. The septa are hexamerally arranged in four complete


cycles: S1–2>S3>S4 (48 septa), even in coralla as small as 6.0mm GCD. S1–2 are exsert, their axial edges quite sinuous, and their lower axial edges fused to the lamellar columella. The S3 are about four-fifths the width of the S1–2, much less sinuous, and they fuse with the columella. The S4 are two-thirds the width of the S3, their axial edges not attaining the columella. The fossa is deep and contains a prominent sharp lamellar columella, characteristic of the genus (Fig. 2.11, 2.12).


Materials.—USGS 10674, Muddy Creek, Victoria, Balcombian (middle Miocene), 39 coralla, USNM 77069 (topotypic). Clif- ton Bank, Muddy Creek, Victoria, Balcombian, eight coralla, USNM 67956 (topotypic). Grice’s Creek (near Frankston), Victoria, Balcombian, six coralla, USNMM353579. Sunnyside Beach (Grice’s Creek), Mornington, Victoria, Balcombian, 1 corallum, USNM 1283880. USGS 10808, Torquay, Janjuk Creek, Janjukian (late Oligocene), one corallum, USNM 1283878. Bird Rock Cliff, Torquay, Janjukian, two coralla, USNM 1283879.


Remarks.—Periplacotrochus elongatus is easily distinguished from other species by its elongate slender corallum (GCD: H =1.6–3.2) (see also the Key in Table 2).


Periplacotrochus pueblensis (Dennant, 1903) new combination Figure 2.13–2.15


1903 Placotrochus pueblensis Dennant, p. 212, pl. 2, fig. 1a–b. 1981 Placotrochus pueblensis; Bell, p. 11 (type deposition). 1989b Placotrochus pueblensis; Cairns, p. 75 (mentioned).


Types.—The holotype is deposited at the NMV (P27106). Type locality: Spring Creek (The Ledge), Victoria, Janjukian (late Oligocene).


Diagnosis.—Corallum with four cycles (48 septa) of hexam- erally arranged septa; corallum straight to irregularly bent (but not cornute); calice round in cross section.


Occurrence.—Known only from the type locality.


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