Shell small for the genus, postnuclear whorls 3.5. Nucleus of one flattened whorl, 1st postnuclear whorl developing a single angular carination that lasts only 2/3 of one turn. Later whorls rounded, suture descending on final whorl, the immediate subsutural area on the final whorl flat or slightly concave. Later whorls sculptured with fine, even spiral striae, approximately 15 striations exposed on the penultimate whorl above the termination of the lip, 6 on the whorl directly above. Aperture proportionately large, nearly circular, outer lip thin, inner lip bordering a narrow umbilical chink; in basal view, the extremely narrow umbilicus is partially obscured by the inner lip. Color whitish-pink, with wavy and sometimes interrupted axial striping of darker pink, a slight whitish blotching on the back side of the last whorl. Height, 2.1, diameter, 1.7 mm.

Eulithidium diantha, the only species of Eulithidium known to occur at the Galapagos Islands, differs from all other eastern Pacific species in its color pattern of dark pink markings on a lighter pink ground, emphasized by the name, pink. The operculum (AHF 193-34) is calcarous, white, with microscopic striae running perpendicular to the outer edge. Although most of the type lot is consistently colored like the holotype, some of the lots show a predominance of pink spotting or broad white banding or mottling.

Type Locality: East of south end, Albemarle (Isabela) Island, Galapagos Islands, Ecuador, 0° 55' S, 90° 30' W, 60 fathoms, R/V Velero III bottom sample station 450, 26 January 1934, 54 specimens, none live-collected.
Type Material: Holotype, LACM-AHF 1397: 37 paratypes, LACM-AHF 1398. Two paratypes each, AMNH, ANSP, CAS, MCZ, SBM, SDNHM, SU and USNM.
Referred Material: AHF 193-34, Post Office Bay, Charles Island (Santa Maria), 8-10 fathoms, 2 specimens with operculum in place. Additional specimens are represented from AHF bottom sample stations 401, 402, 429, 430, 435 and 464, including San Cristobal, Santa Maria, and Wenman Islands, at depths ranging from 9 to 150 fathoms.