to be added
“The new species is related to Opisthostoma (Plectostoma) charasense Tomlin and O. (Pl.) laidlawi Sykes. From O. (Pl.) charasense it differs in the greater size, the narrower spire and the more numerous vertical ribs.” (Benthem-Jutting, 1961)
Apex. Shape: distinctly convex.
Spire. Height: 2.0–2.2 mm. Width: 1.8–2.0 mm. Number of whorls: 4 1/4–4 5/8. Apical spire shape: depressed conical. Basal spire shape: conical. Whorl periphery: moderately to distinctly convex. Umbilicus: open.
Constriction. Parietal teeth: two. Basal teeth: none.
Tuba. Coiling direction: type 2 and aperture visible in right lateral view. Tuba whorl length in proportion to spire last whorl: ca. 5/8–7/8. Proportion of tuba that attaches to spire: more than 1/3 but less than 1/2.
Aperture and peristome. Peristome: double peristomes. Outer peristome shape: similar to inner peristome, projected all around, except the posterior part, where the left lateral sides are slightly more projected than the anterior and right lateral side.
Spiral lines. Thick lines: absent. Thin lines: present.
Radial ribs. Rib density: 6–7 ribs per mm. Rib intensity: thin. Shape: slightly curved. Inclination: moderately prosoclin.
to be added
Holotype: ZMA 136034(1) (Seen). Paratypes: ZMA 136041(>50) (Seen), ZMA 136042(>25) (Seen).
There is no genetic information for Plectostoma praeco. Morphological similarity suggests thatPlectostoma praeco and Plectostoma tenggekensis are closely related. Each of the two species has a narrow distribution range and they are separated from each other by at least 50 km.
Type locality. Batu Che Derani, Taman Negara Pahang (4°35'57"N, 102°25'57"E).
Distribution range. Plectostoma praeco has been recorded from four other hills at upper Sungai Keniyam Kecil, which is in the vicinity of the type locality (Figure 18B).
Least concern. All the limestone hills where Plectostoma praeco occurs, are located in the National Park.
ZMA 162150(>100), ZMA 162151(>100), ZMA 162152(>100), ZMA 162153(>10).
Shares with Plectostoma laidlawi, Plectostoma tenggekensis, and Plectostoma annandalei the general shell form, in terms of spire and tuba shape, but differs by having slightly curved ribs.
Benthem-Jutting (1961) original descriptions on Opisthostoma (Plectostoma) praeco – “Shell with regular, broad-conical spire, ending in an abnormally coiled and detached last whorl, with a trumpet-shaped aperture. At the transition of the regular spire into the abnormal terminal part the whorl is transversely constricted. White or very light-pink, shing and somewhat transparent. First 1 ½ whorls smooth, following ones ornamented with delicate, oblique, transverse, white ribs, standing away wing-like from the shell. There are 30 ribs on the last normal whorl before the constriction. After the constriction the ribs stand wider apart. In the holotype there are 12 ribs between the constriction and the aperture, a distance of 2 ½ mm. There is a delicate spiral striation. Whorls 6 (the detached trumpet not included), convex. Suture deep. The convexity is accentuated by the wing-like ribs. Top pointed, but not sharp. Base rounded. Umbilicus distinct and deep, but not wide. Last whorl irregular, transversely constricted in the middle, then widening towards the aperture, at the same time turning back and a little upward, free from the spire. Aperture facing obliquely up and back, thus falsely suggesting a sinistral shell. Aperture round. Peristome continuous, circular. Just behind the peristome, and parallel with it the terminal part of the trumpet bears a wing-like collar. Operculum unknown.”
The shell is small, white or pinkish white, shining and somewhat transparent with broad-conical spire and circular in cross-section. Whorls six (tuba is not included), convex with deep suture. The first one and half whorl are smooth, and following whorls ornamented with thin, oblique, transverse, white, and wing-like ribs which and widely spaced (four ribs/0.5 mm on the penultimate whorl and five ribs/0.5 mm on the body whorl close to the constriction). Umbilicus is narrow and approximately 0.25 mm across. The body whorl is irregular and constricted with transverse palatalis. The tuba is completely detached after the six whorls, turning back and projecting a little upward. Aperture is ovate with continuous and double rounded peristome which is detached from the spire. Operculum is unknown. The shell height is between 2.4-2.0 mm, the total width is between 3.0-2.8 mm, and aperture diameter is between 1.2-1.0 mm.
Opisthostoma (Plectostoma) praeco – “Dimensions: Height 2.0-2.4, Breadth 2.8-3.0, Diam. apert. 1.0-1.1 mm.” (Benthem-Jutting, 1961)
Type locality – “Malaya: Batu Che Derani, Ulu Kenyam Kechil, Pahang” leg. J. R. Hendrickson (Benthem-Jutting, 1961)
Other localities – “Malaya: Ulu Kenyam Kechil, Ulu Tembeling, Pahang” leg. J. A. Hislop (Benthem-Jutting, 1961)
PAHANG - Taman Negara; Batu Che Derani, Ulu Keniam. (Leg. J.R. Hendrickson/1954); Ulu Kenyam Kechil, Ulu Tembeling (Leg. J.A. Hislop/1952); Limestone outcrops (Batu Kambing, Tomoh Bengong, Batu Landak, & Gua Chiak), all in Ulu Kenyam Kechil (Leg. University Malaya/1954-1958)
