Shell up to 3.40 mm wide, about as broad as high, rather thick, narrowly umbilicate, nacreous white. Protoconch of 1 convex whorl; very fine, crisp, irregularly anastomosing dendritic sculpture throughout. Teleoconch of up to 5.25 whorls; spire whorls shallowly convex or flat; periphery angulate; base suddenly contracted, shallowly convex. First 2 whorls medially angulate, completely covered with fine, crisp, anastomosing dendritic threads. Sculpture vanishing over next half-whorl. Subsequent whorls smooth apart from the peripheral spiral, itself smooth, most of which is exposed on the spire. Base smooth apart from a few spiral threads below periphery and bordering umbilicus. Aperture subquadrate. Outer lip simple within; basal notch shallow; no posterior or peripheral notch. Inner lip thick, simple, spreading on to wall of umbilicus.

Thelyssina sterrha closely remembles the type species of Thelyssa Bayer (1971) (T. calliosto Bayer, 1971) in shape and size, but differs in lacking collabral axial riblets and a posterior notch, and in having peculiar dendritic sculpture on the early teleoconch whorls. Basilissa simplex Watson, 1879 and B. munda Watson, 1879 closely resemble T. sterrha, and may well prove to be congeneric with it.
Bayer (1971) distinguished Thelyssa from Basilissa (type species B. superba Watson, 1879) primarily by the presence of a septum that completely covers the umbilicus at maturity. Although the umbilicus is open in the originally unique holotype of B. superba (Watson 1886, p. 101, pl. 7 fig. 10; Cernohorsky 1978, p. 33, pl. 8 fig. 4), Okutani (1982) has reported that specimens recently collected off Japan have a thin septum that covers two-thirds of the umbilicus. Apart from seemingly minor details of shape and sculpture, the only major difference seems to be in size, B. superba attaining about 4 times the height of T. calliosto. I have little doubt that Basilissa and Thelyssa are distinct genera, yet they may prove to be more closely related than was hitherto anticipated.