Figures 2F; 5G–I; 7C; 10D.

Type material

Holotype: AMS C.439672, Damper Cave, main streamway, stn 6, 22, DEC, 1991.

Paratypes: AMS C.201496, Damper Cave, main streamway, stn 6, 22, DEC, 1991 (3 dry, 2 wet); AMS C.203681, Damper Cave, streamway near entrance, stn PB1–1A, 28, MAR, 1994, 4 dry, 1 wet); QVM, 9:20537 (1 dry).

Etymology Auris Latin, ear; forma Latin, shape; refers to the ear­shaped aperture.

Description

Shell. (Figs 2F; 5G–I). Length up to 4.4 mm; conical (SW/SL 0.59–0.65, mean 0.63, n = 6); spire moderate to high, straight in outline; last whorl evenly rounded, or angular to subangular in middle of whorl; suture indented/impressed, grooved/channelled or with very narrow shoulder above or below; subshoulder depression on last two whorls. Protoconch microsculpture unknown. Teleoconch up to 3.8 whorls in adult; aperture oval to pear­shaped; large, about equal to spire (AL/SL 0.47–0.55, mean 0.52, n = 6); outer lip prosocline, thin to weakly thickened in adult, straight, with strong reflection; external varix absent; notch usually present in posterior corner of aperture; upper half of inner lip thin to moderately thickened and moderately wide, thicker in lower half, in partial contact or narrowly separated from parietal wall. Translucent, semi­opaque; white (semi­opaque to opaque), or yellow.

Dimensions. See Table 4.

Operculum. Yellowish or brown; inner surface with or without white smear.

Pallial cavity (Fig. 8C). Ctenidium narrow; 14–15 very small filaments; osphradium between posterior end and middle of ctenidium to near middle of ctenidium; hypobranchial gland thick; renal organ extends forward ca. ⅓–½ into pallial cavity; pericardium more than ½ in pallial roof.

Radula (Fig. 7C). Central teeth: dorsal edge with shallow indentation; 4–5 lateral cusps, median cusp of medium width, sharply pointed, less than twice as long to about equal to adjacent cusps. Lateral teeth: dorsal edge with shallow indentation; with 3–4 cusps on outer and 3 on inner side; median cusp of medium width, sharply pointed, less than twice as long as adjacent cusps; ratio of cutting edge to shaft about ¼; basal projection bluntly pointed. Marginal teeth: Inner with 15–17 cusps; outer with 15–19 cusps.

Stomach. Stomach with posterior chamber and anterior chamber about equal in size, or with posterior chamber a little smaller than anterior chamber.

Male genital system. Testis of 1.5–2.0 whorls; prostate gland oval to kidney­shaped; compressed in section. Pallial vas deferens straight. Penis with weak swelling in mid­distal portion; distal end long, papilla­like; medial section parallel sided, of medium length; penial duct in medial section of penis straight to slightly undulating; base of penis moderately wide, or narrow; with weak to moderate folds; penial duct straight to undulating.

Female genital system. (Fig.10D). Ovary of 0.9–1.2 whorls; oviduct extends to posterior edge of bursa copulatrix or slightly anterior to that edge; with or without one bend distal to seminal receptacle; joins bursal duct in front of posterior pallial wall about half way between posterior pallial wall and capsule gland to about junction of albumen and capsule glands. Bursa copulatrix large, slightly in front of posterior pallial wall to slightly behind; pyriform to elongately oval; with bursal duct arising from middle of anterior edge of bursa; straight or with bend. Seminal receptacle at middle of inner wall of bursa copulatrix or near mid ventral edge; ovoid to pyriform. More than ½ of albumen gland in front of posterior pallial wall; capsule gland longer than albumen gland; compressed oval in section; anterior end tapering to blunt; ventral channel simple, approximately parallel­sided throughout; vestibular area distinct; genital opening overlapping anterior end of capsule gland.

Distribution and habitat

Known only from the main streamway in Damper Cave. This streamway is wider (about 2m) and has a faster flow (estimated at 10–20L/s) than the streams in which P. expandolabra occurs. The substrate consists of cobbles and gravel.

Remarks

Pseudotricula auriforma is similar to P. expandolabra but differs mainly (P<0.001) in its larger, more slender shell. It lives in a streamway that is wider and faster flowing than any of the habitats in which P. expandolabra occurs and the substrate lacks fine sediments.