Description. —- See Laseron (1951). Shell elongate, subcylindrical, whitish, fragile and with a clear separation between the upper and lower parts of the whorls. Protoconch short with only one whorl and a diameter between 160 and 173 µm. Nucleus very small, about 15 to 20 µm. The first whorl of the teleoconch has about eight or nine series of small, almost rectangular pits that are spirally arranged without an evident separation between upper and lower parts of the whorl. At 3/4 of this whorl the separation (formed by a furrow that commenced a little before this point) becomes more distinct as the furrow widens to a distinct shelf that offsets both parts like a step. The subsutural area (approximately 30% of the height of the whorl) is rather smooth, but whereas immediately below the suture some axial striae or a rough area can be seen and sometimes also scarce very fine spiral striae, the lower half of this area is practically smooth with only very fine opisthocyrt lines. The lower part of the whorls has very weak, prosocyrt growth lines. The sculpture of the lower part of the whorls is formed by 5 to 14 spiral furrows that vary in width and number and are formed by depressions that also vary in intensity and shape but increase in size as the whorls become larger. Under higher magnification a microsculpture of small pits can be seen inside the depressions . Aperture rounded, with sharp peristome; there is a narrow umbilical fissure.
Distribution. — This species was found in Fiji, Solomon Islands, New Caledonia, Philippines and Japan. Probably it lives in the whole Western Pacific. Numerous specimens were collected in the Philippines, between 3 and 33 m water depth.
Remarks. — This species is rather variable: even within a single population shells occur with only a few or numerous spiral furrows. The holotype has numerous spirals. Several shells from different Pacific populations are figured.
This species can be distinguished from other species because the protoconch has only one whorl and the nucleus is small. Also the conspicuous step that separates the two parts of the teleoconch whorls and the sculpture of spirally arranged pits is not present in the species described above.
The apical whorls of specimens from Fiji are similar to those from other places but the lower whorls sometimes show weaker spirals. Shells from the Solomon Is. and the Philippines are larger but without any other variation.
Murchisonella arabica is easily distinguished by the cord marking the separation, the sculpture of the upper part of the whorls and the predominant axial sculpture.
Murchisonella anabathron has a larger and more elongate shell and a less distinct separation, not angled, between the two parts of the whorls. The sculpture of the lower part is formed by continuous furrows without perforations, and the subsutural part is almost smooth and only under high magnification small striae can be seen on the lower part of the subsutural area; the protoconch has a larger "nucleus".
Murchisonella curvistriata spec. nov. has a more conical profile and the teleoconch whorls are more convex with weaker separation between the two parts. The sculpture is delicate: in the lower part of the whorls it is formed by numerous, shallow, almost imperceptible furrows and the growth lines are more conspicuous. The protoconch has a larger "nucleus".