Description: Shell minute, turbinate, deeply umbilicate, aperture and whorls circular, peritreme complete, suture deeply impressed, lip thin. Whorls 3.4 to 3.7; axial sculp¬ture of irregular growth increments only; spiral sculpture of 35-53 flat-topped cords on final whorl; spiral cords increasing in number by emergence between existing ribs; ribs faint near suture, strong and with narrow interspaces on upper surface of body whorl, with broader interspaces on lower surface. Color white to light tan, surface often stained rust to black. Operculum calcareous, multispiral, outer surface concave, with 6 evenly expanding volutions, not retracting within aperture. Dimensions: Holotype: height 1.82 mm, diameter 2.24 mm; height 81% of diameter.

Spiromoelleria kachemakensis has a higher spire (shell height 81% of diameter, compared to 68%), a narrower umbilicus, and more prominent spiral cords than S. quadrae. There are no intergrading specimens.
The small turbinid Homalopoma lacunatum (Carpenter, 1864), which occurs from Alaska to Washington, differs in having a larger, thicker shell, a less impressed suture and opercular volutions that are paucispiral.
We have no records of the three species occurring at the same station, as Spiromoelleria quadrae has been taken only intertidally and Moelleria costulata only subtidally in Kachemak Bay. However, S. quadrae and S. kachemakensis were collected together at low tide (near the type locality of S. kachemakensis) at the west end of Yukon Island, Kachemak Bay (59°31.5'N, 151°29.5'W) by Baxter & McLean in August 1973. Living specimens of M. costulata were collected offshore with S. kachemakensis at the type locality.
MACNEIL et al. (1943) illustrated an eroded fossil specimen of Spiromoelleria from a raised terrace at Nome, Alaska, which they identified as "Mollena n. sp.?" Al¬though its proportions are similar to those of S. kachemakensis, the specimen (USNM 499052) is much larger (dimensions: height 2.96 mm, diameter 3.40 mm) than known for S. kachemakensis. In size it is comparable to Homalopoma lacunatum, but it has the deeply impressed suture of the genus Spiromoelleria. We refrain from further treating this specimen in the absence of more and better preserved material.

Type locality: 9 m on mud-shell bottom, off northwest side Hesketh Island, Kachemak Bay, Cook Inlet, Alaska (59°30'31"N, 151°30'01"W). The name of the species is based on the type locality.

Distribution: Kachemak Bay, Cook Inlet; along the Kenai Peninsula; Prince William Sound; east to Rush Bay, Glacier Bay, southeastern Alaska (58°28'N, 136°04'W) (UAF M2671, collected by George Mueller). Not collected at Kodiak Island or to the west. Living specimens have been collected by Baxter at or near the type locality and at Port Dick on the south side of the Kenai Peninsula (59°13'N, 151°03'W). Living on undersides of rocks at low tide to 45 m on gravel or muddy, shell bottoms, par¬ticularly at the base of vertical drop-offs.