Shell minute, inequilateral and inequivalve, white, fragile, the two valves with discrepant sculpture. Left valve sculptured with weak concentric raised threads, crossed by distant weak radials, both becoming obsolete over outer third of shell surface; concentric threads about 5 per mm. Ears subequal, not clearly defined from disc, anterior ear with fine concentrics, posterior ear with very fine radials. Right valve with closely spaced concentric lines about 14 to 15 per mm., interspaces with very fine interstitial radials. Both ears with fine concentrics, anterior ear clearly marked off from disc by a groove, a well-defined byssal notch. Length, 4-0 mm.; height, 4-3 mm.; inflation, 0-73 mm. (right valve); length. 4-5 mm.; height, 4-5 mm.; inflation, 0-82 mm. (left valve).
C. powelli is closest to Cyclochlamys aupouria Powell which has comparable sculpture. From aupouria it differs in the finer (though less closely spaced) concentric ridges in the left valve and obsolete radial sculpture over the latter half of the shell. In addition the radial sculpture in this valve consists of threads which cross the concentrics rather than the small, dense interstitial radials of aupouria.