Shell small (to 12.0 mm), broadly fusiform, with a large asymmetric body whorl approximately 59% of total length, of 9 convex whorls with impressed sutures, shell slightly translucent (in part), surface glossy. Protoconch of approximately 2 smooth whorls, the first free, not immersed. Axial sculpture of broad straight ribs with round crests that extend from suture-to-suture on spire whorls, narrowest at suture then broaden at whorl periphery and fade at the suture line; absent from the mid to lower portion of last whorl. There are from 9-11 ribs on the penultimate, 8-10 on the last whorl. Sulcus absent, but ribs slightly narrower and somewhat pinched and curved on shoulder. Varix like a greatly enlarged rib, cup handle-like, adjoins the rear of anal sinus about 1/4-turn from the edge of the outer lip. Spiral sculpture absent except for faint spiral ridges on base, stronger on anterior fasciole. Outer lip thin, a short projection from the varix with a narrow strengthening rib just before lip edge; lip edge forming a low arc congruent with the anal sinus to the anterior canal; stromboid notch a shallow and wide indentation and slight wave of the lip edge. Anal sinus U-shaped, deep, located on shoulder a little below suture; parietal lobe projects into the sinus. Inner lip narrow, detached anteriorly, thin and attached on the parietal wall; forming a parietal lobe posteriorly. Anterior canal straight, short; without a notch; anterior fasciole not swollen. Color varies between specimens, a uniform white to off-white, pale to dark amber, and brownish orange.

Cerodrillia ambigua is morphologically typical for the genus: a broadly fusiform shell, a large body whorl with a relatively short spire, and a large varix positioned laterally giving the shell a lopsided appearance when viewed ventrally. Its axial ribs are unique, their profile an almost perfect arc, but absent on the shell base, ending at the suture line. Variability. The average total length of 48 measured shells is 9.12 mm (4.7-12.0 mm); their average W/L ratio is 0.446. The color of examined specimens varies from a solid white to solid golden brown. No color patterning is evident. Identification. Among its congeners most likely encountered off E Florida, C. ambigua differs from C. perryae Bartsch & Rehder, 1939 and C. thea (Dall, 1884) in possessing broader ribs with round crests and ribs only slightly changed on the whorl shoulder The ribs of C. thea are shorter and oblique. Ribs are lower, narrower, and arched on the shoulders of these two. From Douglassia bealiana Schwengel & McGinty, 1942 it differs in possessing straighter ribs, less angular shoulders, in lacking spiral color bands, and has a protoconch with only two whorls, not three. From C. girardi Lyons, 1970 it differs in having a proportionately less globose body whorl, and more rounded shoulders.

E Florida (Duval Co.; St. Johns Co.; Palm Beach Co.). Reported at 37-183 m.