As Aclis bermudensis:
Shell minute, elongate-conic, white, subdiaphanous. Nucleus com-posed of a single turn which is well rounded and smooth. Post-nuclear whorls strongly shouldered on the early turns, the shoulder forming a prominent carina at the anterior termination of the pos¬terior two-fifths of the space between the sutures. The surface of the shell between the anterior suture and the shoulder is marked by six equal and equally-spaced very slender spiral threads, while the space between the shoulder and the summit is smooth. Beginning with the fifth whorl the shoulder becomes less apparent and finally loses its angulation altogether. The posterior two-fifths between the sutures, however, remains smooth, while the anterior three-fifths retains the six raised threads. Entire surface of the shell marked by exceedingly fine incremental lines. Sutures strongly constricted. Periphery of the last whorl feebly angulated. Base short, moderately rounded. Aperture subquadrate, somewhat effuse anteriorly; posterior angle obtuse; outer lip very thin, showing the external markings within; columella almost straight and slightly revolute.
The type has seven post-nuclear whorls and measures: Length, 2.1 mm.; diameter, 0.6 mm. It was collected in Bermuda and is in the Bermuda Museum. The minute sculpture is not indicated on the figure.

Faber (2005) repeats the original description and describes the type material. The upper part of the whorls is about 40% of the whorl height. The separation is not very prominent but evident. The lower part has spiral furrows variable in number and in distribution. Dimensions: shell height usually 2 mm. Some shells from our material (Cuba) measure nearly 3 mm in height.
Distribution. — According to Faber (2005) the species is known from all the Caribbean area (ABC Islands, Florida and Virginia, USA, Bahamas, Salvador, Cuba, Jamaica, Dominican Republic, Virgin Islands, Belize, Honduras, Venezuela and Grenada). We have material from Nicaragua, Guatemala, Mexico and Cuba. These references show that the species is widely distributed throughout the Caribbean Sea. Rios (1994, 2009) recorded it from the north of Brazil. Redfern (2013: 698) illustrated shells from Abaco, Bahamas.
Remarks. — In spite of the existence of several species names in the Caribbean we could not find clear and constant differences in the material studied and therefore no evidence that more than one species occurs in this area.
Redfern (2001) figured two shells of M. spectrum: fig. 631A is the typical form of M. spectrum and M. bermudensis, while figure 63IB has a more conical profile (PI. 1, Fig. 6A-C) with less convex whorls of which the last one is more angled at the periphery; this form could also be different to the one called M. tampaensjs. It could be a deformed shell, because the first whorls have a different curvature from the later ones. We have no other material with these characteristics. In Redfern (2013) these photographs are reillustrated.
The topotypes of M tampaensis (USNM 466295) are not noticeably different from M. spectrum therefore we consider both taxa synonymous.
Bartsch (191 IB) described and figured Aclis floridana from deep water of Florida (150-200 ft) and made a comparison to A. bermudensis. In our opinion both are different species: A. floridana must be included in the family Aclididae. Bandel (2005: fig. 32) figured a young Murchisonella from the Caribbean which he identified as "Murchisonella floridana". He also considered Aclis floridana to be the type species of Schwengelia, but A. hendersoni Dall, 1927 is the true type species. We examined the type of Aclis floridana (USNM 82973a) (PI. 2, Fig. 6D-E) which is not in a very good condition, but its protoconch is pupoid and for this reason we consider it an Aclis and not a Murchisonella.