Phaedusa filicostata stenotrema Thompson & Dance, 1983
“Phaedusa filicostata (Stoliczka) includes six other subspecies (Loosjes 1953: 38-53). Five are confined to the Malayan Peninsula. One, P. f. filialis (von Martens) is found in southeastern Kalimantan, Borneo. P.f. stenotrema is most similar to P. f. tenuicosta (Nevill), a subspecies widely distributed in the Malayan Peninsula. It differs from tenuicosta by its usually smaller size, relatively more obese shell with a lower L/W ratio, lower whorl count and narrower aperture in which the outer lip is straight-sided or slightly concave in outline. In addition the axial riblets of stenotrema are nearly straight in contrast to the wavy riblets of tenuicosta. Loosjes gae measurements for eleven population samples of tenuicosta. His sample of smallest specimens from Kelantan are as narrow as stenotrema, but they are longer and have a higher whorl count. P. f. filialis has little similarity to P. f. stenotrema. It is a much larger subspecies with flat whorls and heay palatal plicae (Loosjes 1953:50-53). P. f. stenotrema is sympatric with P. borneensis (Pfr). The latter is distinguishable from stenotrema by its swollen neck and its more rugose sculpture.” (Thompson & Dance, 1983)
Thompson & Dance (1983) original descriptions on Phaedusa filicostata stenotrema – “Shell terrete-fusiform, sides of spire slightly convex, nearly straight-sided, medium-sized, about 17-21 mm long, anout 4.28-5.26 times as long as wide. Lower whorls narrow, last three whorls comprising 0.62-0.67 length of shell. Brown in color, barely transparent, shiny; interior of aperture light brown; peristome white. Whorls 9.5-11.2, weakly arched with a moderately impressed suture. A barely visible subsutural spiral cord occurs along lower whorls. Embryonic shell with 3 whorls, sculptured with fine thread-riblets that weakly crenulated the suture. Following whorls sculptured with similar oblique thread-riblets that are frequently poorly defined. Riblets becoming stronger and more widely spaced on last whorl. Penultimate whorl woth 10-15 thread-riblets/ mm; back of last whorl with 8-11 riblets/mm. Aperture sub-elliptical, narrow, about 0.68-0.75 times as wide as high; free from and projecting forward from previous whorl. Plane of aperture nearly parallel to axis of shell. Peristome broadly expanded, narrowest above sinulus, widest along basal lip. Edge of outer lip straight-sided or weakly concave. Sinulus slightly deeper than wide, pointed at apex. Superior lamella thick, oblique, slightly converging toward outer lip, short, confined to parietal edge of aperture, widely separated and offset to the conter from spiral lamella. Inferior lamella extending into aperture for one whorl, converging toward, but separated from upper end of spiral lamella; inferior lamella gradually decreasing in height posteriorly and anteriorly where it flexes to descend partially down columellar side of aperture. Columellar lamella lower and shorter than inferior lamella, not visible from aperture. Spiral lamella about as high as inferior lamella; oblique, sloping toward principal plica; spiral lamella beginning on parietal wall ¼ whorl behind aperture and continuing for ¾ whorl to ventral side. Principal plica extending from middle of right side to a little to left side in a crescent that may be on a lunella-like callus. Upper palatal plica about 1/3 as long as principal plica and diverging from it. Lowest plica short, and oblique. Other plicae short and tubercular or absent. Clausilium plate 2.1 mm long, 1.3 mm wide; sides iverging to widest point about 1/3 of distance from end, weakly pointed and folded. Pedicel long and slender, lying at about 70° to plate (clausilium from specimen 19.5 mm long).”
Phaedusa filicostata stenotrema – “Length 19.1-20.5, width 3.9-4.0, aper. h. 4.4-4.6, aper. w. 3.2-3.4, whorls 9.5-11.2.” (Thompson & Dance, 1983)
Type locality – “Melinau Limestone, near Gunong Mulu, lower Tutoh Valley, Fourth Division, Sarawak, Borneo, 04°03’N, 114°48’E” leg. G. E. Wilford/1961 & S. P. Dance (Thompson & Dance, 1983)