(Figs 15B–D; 16B–D; 17B–D; 18A–C; 19B–D; 20F; 21F; 22F; 23F; 24E; 25A, B; 26A, B; 27C–G)

Gyrocochlea hawkesburyana Stanisic, 2010: 196 (in Stanisic et al. 2010).

Diagnosis. Shell very small, pale orange to cinnamon-brown, biconcave with weakly to strongly depressed spire. Protoconch sculpture strongly spiral consisting of 28 to 30, prominent, closely spaced, beaded spiral cords.Teleoconch sculpture of numerous, prominent, quite uniformly spaced, slightly sinuate, orthocline radial ribs. Ribs on body whorl 69–150. Umbilicus wide cup-shaped. Penis tubular, internally with a conical to loop-shaped apical verge and longitudinal pilasters tapering to the atrium; verge opening through a lateral slit

Type material examined. Holotype. AM C.171393, Brooklyn, N side of Brooklyn Rd, Seymours Ck, ca. 100m from Pacific Hwy, NSW (33° 33’ 04” S, 151° 11’ 49” E), 7.viii.1983, coll. M. Shea. Paratypes. AM C.472883, same data as holotype.

Other material examined. (All Sydney Basin, NSW) Brooklyn: AM C.346888, AM C.462512, AM C.462496. Turramurra: AM C.318933. Calna Creek: AM C319719, AM C.462434, AM C.462492, AM C.462515. Parriwi Park: AM C.462551, AM C.462552. Mount Wilson: AM C.26351, AM C.63749, AM C.140458, AM C.171394, AM C.360850, AM C.463091, QMMO 28769.

Description. Shell very small, pale orange to cinnamon-brown, biconcave with weakly to strongly depressed spire. Whorls 3.12–4.12, tightly coiled, the last inflated and descending in front. Sutures strongly impressed. Shell diameter 2.60–3.68 mm (mean 3.13 mm), height 1.30–2.00 mm (mean 1.64 mm), H/D 0.45–0.55 (mean 0.52). Protoconch flat, of 1.25 whorls, diameter 0.37–0.60 mm. Protoconch sculpture strongly spiral consisting of 28 to 30, prominent, closely spaced, beaded spiral cords and weak closely spaced radial ridges becoming more pronounced toward the protoconch-teleoconch boundary. Teleoconch sculpture of numerous, prominent, quite uniformly spaced, slightly sinuate, orthocline radial ribs. Ribs on body whorl 69–150 (mean 98), width of interstices on the first teleoconch whorl greater than or equal to width of four and six ribs; on the penultimate whorl equal to width of four to less than six ribs;each rib with two or more overlapping periostracal blades. Interstitial sculpture of low prominent microradial ribs and low, weaker microspiral cords forming weak beads at their intersection; number of microradials between ribs on the first teleoconch whorl 5–8; on first quarter of body whorl 5–9; height of microspirals variable. Aperture broadly ovately-lunate. Parietal callus prominent, transparent. Umbilicus wide cup-shaped, diameter 0.76–1.12 mm (mean 0.95 mm), D/U 2.86–4.04 (mean 3.33). Based on 33 measured adults.

Reproductive organs with ovotestis containing two clumps of alveoli, with more than two alveolar lobes per clump. Hermaphroditic duct narrow crescent-shaped. Spermatheca with a medium to large-sized oval bulb.Talon large, circular or oval shaped. Penial retractor muscle less than half the length of penis, inserting at the junction of the penis and epiphallus. Epiphallus equal or subequal in length to the penis. Penis tubular, internally with a conical to loop shaped apical verge and longitudinal pilasters tapering to the atrium; verge opening through a lateral slit. Vagina shorter than penis.

Distribution and habitat. Broken Bay (Brooklyn), and Middle Harbour, Port Jackson to Mt Wilson, Sydney Basin, NSW; found in dense sclerophyll forest, dry rainforest and warm temperate rainforest, particularly in gullies and along watercourses, living under rocks and logs.

Remarks. P. hawkesburyana is similar to P. watagan n. sp. in shell morphology but differs most noticeably in having fewer ribs on the teleoconch

There is considerable variability in spire depression and rib spacing on the teleoconch of the various samples of P. hawkesburyana. This may be environmentally-induced variability or reflect on-going lineage differentiation in isolated populations. In particular, the Brooklyn site is distinguished from the others of the species in verge anatomy. In Brooklyn specimens, this is an open sculptured loop or scoop-shaped structure fused to the wall of the penis just below the epiphallus entry, whereas specimens from other sites have a bud-shaped papilla with internal parallel ridges inside the penis. Shells from this site also have more widely spaced and stronger radial ribs on the teleoconch and finer spiral threads on the protoconch. The various specimens for which DNA material was available were shown to be genetically conspecific.