Figs. 1, 3 K, 5 F, 11 F– 11 G, 13; Tables 2, 3
Type material. Holotype: HBUMM-06089–specimen 3 (fma); Yuxushan Hill, 10 km north of Wenxian, site No. 0 45, 1070 m a.s.l., 32 ° 57 ʹ 35.5 ʹ N, 104 ° 40 ʹ 41.6 ʹ E, Wenxian County, S. Gansu, China, 2006 –IX– 27, leg. M. Wu, J. Liu, W. Zheng & L. Gao. Paratypes: HBUMM-06089–specimens 1, 2 (2 fma, shell partially removed for dissection), 4, 5 (2 fms), same collection data as holotype.
Type locality. Yuxushan Hill, 10 km north of Wenxian, Wenxian County, S. Gansu.
Material examined. Type material.
Distribution. Gansu (only known from type locality).
Etymology. The new species is named after the type locality “Yuxushan”. The epithet is a noun in apposition.
Diagnosis. Shell with 6.750–7.500 whorls. Height 6.2–6.7, diam. maj. 2.6–2.9. Parietal tooth present or absent. Columellar tooth invisible from aperture but expanded inwards. Palatal tooth ridge-like. Epiphallus forming a few loops. Flagellum present. Penial caecum present. Penis distally without V-shaped pilasters, with two thick, parallel pilasters connected at distal end. A- 2 near A- 3 internally with a ring of papillae. A- 3 opening into A- 2 without papilla. Bursa copulatrix duct proximally twisted. Diverticle present.
Shell. Cylindrical with conical top; apex not acuminate; dextral; thin-shelled; solid; translucent or semitranslucent; glossy; with 6.750–7.000 – 7.500 whorls. Whorls never spirally grooved; convex. Embryonic shell smooth; polished; with 1.500–1.650 – 1.750 whorls. Postnuclear whorls wrinkled. Suture simple. Last whorl gradually ascending towards aperture; rounded at periphery. Shell 6.2–6.5 – 6.7 high; 2.6–2.7 – 2.9 in diam. maj. Height/diam. maj. ratio 2.33–2.38 – 2.50. Aperture ovate; almost vertical; its insertions separated; 2.2–2.3 – 2.4 high, 1.8 – 1.8–1.9 wide. Ratio of shell height to aperture height 2.72–2.86 –3.00. Palatal tooth ridge-like, extending inward for ca. 1 / 4 – 1 / 3 whorl. Palatal margin rounded. Peristome expanded; sharp. Parietal callus indistinct. Angular tubercle present. Parietal tooth present (in holotype), or absent (in all paratypes). Columellar margin reflexed; with one prominent tooth expanding inward but nearly invisible from aperture. Umbilicus a narrow slit. Shell, including upper whorls, uniformly corneous-brown; aperture white.
Genitalia. Vas deferens long; of even thickness; entering epiphallus apically at an angle. Epiphallus long; cylindrical and of uniform thickness; forming a few loops. Epiphallic caecum apically blunt. Flagellum present; short; tubular; proximally not expanded; with pointed tip. Penis evenly thick; with pilasters fused at epiphallic pore forming velum; without V-shaped pilasters; the two thicker parallel pilasters distally connected. Penial caecum saclike; situated at boundary between epiphallus and penis. Penial verge absent. Penial appendix short; branched off from proximal portion of penis; divided into sections A- 1 +A- 2, A- 3 and A- 4 +A- 5. A- 1 short; without verge toward penial chamber; with longitudinal pilasters. A- 2 internally with longitudinal pilasters. A- 1 and A- 2 fused. A- 2 near A- 3 internally with a ring of papillae. A- 2 and A- 3 not fused. A- 3 opening into A- 2 without papilla. Boundary between A- 4 and A- 5 indistinct. A- 5 short; straight. Atrium with short atrial retractor. Free oviduct short; subequal to vagina in length. Bursa copulatrix duct long; proximally twisted. Bursa copulatrix well defined. Diverticle longer than reservoir; unexpanded. Bursa copulatrix and diverticle distinguishable. Diverticle diverging from bursa duct just proximally from the bursa.
Measurement of genitalia. P: 1.1; Ep: 6.6; Fl: 0.4; VD: 5.7; Va: 0.9; FO: 0.7; BCD: 10.1; BC: 0.8; D: 4.1; A- 1 +A- 2: 0.6; A- 3: 0.8; A- 4 +A- 5: 3.6 (HBUMM-06089–specimen 2, paratype).
Remarks. This species is quite distinct by being the smallest in the genus, by the combination of a columellar tooth and a weak or absent parietal tooth, and by two thick parallel pilasters in the distal part of the penis.