Vaceuchelus: Iredale 1929: 272. Type species: Euchelus angulatus Pease, 1868 [= Monodonta foveolata A.

Adams, 1853], by monotypy.

The shell of Vaceuchelus species is small (length <10 mm), predominantly white and has a cancellate or foveolate sculpture. The aperture lacks a well-developed, peg-like tooth and U-shaped notch at the base of the columella, and may or may not possess denticles inside the outer lip.

Iredale (1929) proposed the genus for Euchelus angulatus Pease, 1868 from the Tuamotu Archipelago, noting that it typified a large series of taxa which differed from more typical Euchelus -like species primarily in lacking a tooth at the base of the columella. It is certainly true that Vaceuchelus species lack the distinctive basal columella dentition of some chilodontid genera, but a number of species still retain some form of apertural dentition. Two subgroupings are evident, namely those which possess denticles inside the outer lip and those that do not. The type species, together with V. foveolatus (A. Adams, 1853), V. scrobiculatus (Souverbie in Souverbie & Montrouzier, 1866) and V. semilugubris (Deshayes, 1863) possess labral denticles, whilst others, e.g. V. cavernosus (Sowerby, 1905), V. clathratus (A. Adams, 1853), V. favosus (Melvill & Standen, 1896), V. gemmula (Turton, 1932), V. jayorum sp. n. and V. natalensis (Smith, 1906), seem to lack all traces of apertural dentition.

To provide a new genus-rank name for such denticle-less taxa would be premature at this stage, since the distinction is based on one character only and, furthermore, there are additional taxa, e.g. V. cretaceus (see below), which present a third, somewhat intermediate facies. Until such time as the data set available allows a more meaningful assessment, I employ Vaceuchelus in its widest sense. Differences in operculum form and protoconch morphology, such as the presence or absence of a sinusigera lip, are also evident, but information is available for too few taxa.

V. angulatus is almost certainly a junior synonym of V. foveolatus (A. Adams, 1853), also from the Tuamotu Archipelago (Pilsbry 1890 in 1889–90). The holotype of the former is somewhat worn, but appears to be nothing more than an elevated and perhaps abnormal example of V. foveolatus in which the upper spiral cord is weakly developed (compare figs 72–73 and 74–75 in Herbert 1996).