BASTERIA, 60: 67-69, 1996

Notes on the non-marine molluscs of the island of Borneo 7.

The Niahia genus gen. nov. (Gastropoda Prosobranchia: Diplommatinidae)

J.J. Vermeulen

Rijksherbarium, P.O. Box 9514, 2300 RA Leiden, The Netherlands

The Niahia is described for N. oberon Next new, monotypic genus spec. nov. to having a unique

the Asiatic it character within SE. Diplommatinidae, displays such a combination ofcharacters

that inclusion in is any existing genus not possible.

Key words: Gastropoda, Prosobranchia, Diplommatinidae, Niahia, taxonomy, Malaysia,

Indonesia, Borneo.

Batu Niah, also known as Gunung Subis, is an impressive, isolated hill in the lowlands of the 4th Division of Sarawak, Borneo. It is situated about 70 kms SSW. of the of its coordinates town Miri; are 113°47'00"E, and 03°47'30"N. The hill consists of limestone of a about outline, and with a surface of outcrop triangular map some 12 km2 Its rises . highest point some 430 m above sea-level; its sides consist of steep or almost perpendicular rock faces, interrupted by ravines cutting deep into the lime- The hill is covered with dense forest. stone. primary It is surrounded by land on a bedrock of sandstone and the closest limestone hill shales; outcrops are a near Bekenu, about 35 kms NNE. of Niah, and some hills near Beluru, about 35 kms ENE. ofNiah.

Other limestone can be found further the the Baram River. outcrops to NE., along all forest Athough surrounding has been logged or otherwise destroyed, most of Batu

Niah itself has the status of National Park and is relatively well protected.

The terrestrial mollusc fauna of Batu Niah is It well extraordinary. may comprise 100 and is different from that of some species remarkably any surrounding limestone hill. Particularly among the smaller, strictly calcicole, species the rate of endemism is The for very high. Diplommatinidae, instance, are represented with 17 taxa (Vermeu- len, 1991, 1993, 1994, in prep.), no less than 11 ofwhich are endemic to this hill. The inner of this recesses deeply eroded karst surface have never been explored; more novelties are to be expected there. A minute found Batu diplommatinid species on Niah, represented in our collections

a shell does fit well in far described. It has by single only, not any genus so a unique character within the SE. Asiatic Diplommatinidae: its inner peristome abruptly widens at the level where the outer peristome is inserted in the shell wall. Inside, this widening is visible the and basal sides of the as a lip on palatal peristome. This lip is not with the the reflected of the inner found in homologous lip on part peristome as many of well few of species Diplommatina Benson, 1849, as as a species Opisthostoma W.T. & H. Blanford, 1860, and Arinia H. & A. Adams, 1865. Its position is also different: it is situated inside the deeper aperture. This character could be regarded as an autapo- the level if the would otherwise fit in morphy on species species any existing genus. This the It lacks the inverted is, however, not case. tuba which characterizes Opisthos- toma; and its distincdy tilted aperture pleads against inclusion in Arinia, in which it 68 BASTERIA, Vol. 60, Mo. 1-3, 1996

would rather well fit otherwise. The lack of teeth in the constriction as well as the

shell inclusion in and the Palaina cylindrical preclude Diplommatina, genus Semper, has 1865, a distinctly longer tuba. Therefore, the species has been accommodated in

new for which the Niahia is a separate, genus, name proposed. Nothing can be said about the phylogenetic value of the genus; it seems, however, to be most similar to

genera such as Arinia, or Palaina.

For the time the of the of being, description type species may serve as a description the well. The instalment of this series the genus as next on non-marine molluscs of Borneo (Vermeulen, in prep.) will complete the revision of the Bornean diplommat- it will include of inids; diagnostic descriptions the genera occurring on the island. The shell available of the described below is of the collection single species part of the author (abbreviated as V, followed by a collection number; the number after the

slash refers to the number of specimens seen). It will be deposited in the Nationaal

Natuurhistorisch Museum, Leiden (RMNH). The made the with Wild M8 drawings were by author, a stereo microscope with a

camera lucida device.

Niahia oberon spec. nov. fig. 1

Material — SARAWAK. 4th Div.: G. Subis seen. (Batu Niah) (V 1506/1, HOLOTYPE RMNH 57206)

Shell white, dextral, shordy cylindrical, last two whorls widest. Whorls 4 1/2, mod- Constriction erately convex. without teeth. Tuba 1/4 whorl. Radial ribs single-crested,

on the whorls and the whorl top on penultimate 36 ribs/0.5 mm, on the last whorl

12 ribs/0.5 ribs absent above the but mm, aperture, present again on most ofthe tuba. Spiral striation absent. Umbilicus seemingly closed but rimate in oblique view. Aper-

1. oberon Fig. a,Niahia spec. nov., holotype specimen, Sarawak: G. Subis (RMNH), front view; b, do., umbilical

view; c, do., right lateral view. Vermeulen: Niahia gen. Nov. from Borneo (Diplommatinidae) 69 ture tilted about 45° with regard to the coiling axis, about ovate. Peristome: palatal side slightly protruding beyond the penultimate whorl, columellar side not sinuous; outer rim not the peristome a very narrow spreading beyond inner, mainly present on the basal and the columellar sides, inner peristome protruding from the outer, abrupdy widened at the level where the outer is attached to the shell wall, and spreading at the margin but without a lip on the palatal and basal side, its outer surface with few fine lamellae. 1.25 width 0.70 index 1.7-1.8. 0.2 Height mm; mm; Height aperture mm; width 0.3 mm.

— Ecology. Calcicole.

Distribution. — Borneo: Sarawak, 4th Div., G. Subis only.

REFERENCES

Notes on thenon-marine molluscs ofthe island ofBorneo 2. The VERMEULENJ.J., 1991. genus Opisthostoma — (Gastropoda Prosobranchia: Diplommatinidae). Basteria 55: 139-163.

1993. Notes the non-marine molluscs ofthe island ofBorneo The , on 5. genus Diplommatina (Gastropoda — Prosobranchia: Diplommatinidae). Basteria 57: 3-69.

1994. Notes on the non-marine molluscs ofthe island ofBorneo 6. The , genus Opisthostoma (Gastropoda — Prosobranchia: Diplommatinidae), part 2. Basteria 58: 75-191.

in Notes on the non-marine molluscs ofthe island ofBorneo 8. The additions to the , prep. genus Arinia;

and Prosobranchia: genera Diplommatina Opisthostoma (Gastropoda Diplommatinidae).