504 MOLLUSCA OP MAST HEAD REEF, QUEENSLAND, II., 



of the upper whorl, thus producing a sharp deep constriction 

 between the whorls. Protoconch large, projecting across the 

 summit of the first normal whorl, and consisting of three prostrate 

 drawn out whorls. Base inflated, well rounded. Umbilicus 

 narrow, partly walled in by the columella. Aperture rhomboidal, 

 rather produced anteriorly, angled posteriorly. Outer lip sharp, 

 medially inflected. Just below the insertion of the columella 

 there projects a single, large, compressed fold. Throat internally 

 finely spirally grooved. Height 2-35 mm.; breadth I'O mm. 



Several specimens from 17-20 fathoms. 



The unusual sulphur colour will aid in the recognition of this 



species. 



Odostomia bulbula, n.sp. 



(Plate xviii., fig.34.) 



Shell small, very solid, imperforate, globose, conical. Colour 

 white. Adult whorls four, rapidly increasing, the last flattened 

 above, subangled at the periphery, rounded on the base. Apical 

 whorls small, wound horizontally, too deeply immersed to count 

 the coils. Sculpture : to the naked eye smooth, but under magnifi- 

 cation ornamented by radial spaced threads, anteriorly wrinkled 

 over a low spiral ridge round the axis. Aperture lunate, outer 

 lip sharp. Columella spreading as a pad over the axis and there 

 bearing a strong, compressed, horizontally-entering fold; below 

 this it is perpendicular, arcuate, much thickened, and slightly 

 reflected, anteriorly meeting the outer lip in a blunt angle. 

 Height 3-5 mm.; breadth 2-75 mm. 



A single specimen from 17-20 fathoms. 



The extreme corpulence of this small Odostomia will facilitate 



its recognition. 



Odostomia sigma, n.sp. 



(Plate xviii., fig.33.) 



Shell small, rather solid, imperforate, ovate, turreted. Colour 

 white. Whorls four, and a heterostrophe protoconch. Sculp- 

 ture : fine, close, ^ regular, radial riblets extending obliquely 

 across the whorls in a sigmoid flexure. Aperture pyriform. 



