Similar in form to P. rutilus (A. Adams), its 7 whorls slightly convex, glossy, and finely and densely spirally striated. Body whorl with angled periphery; base slightly convex. Colour of brownish spots on a pale greenish background, the spots bigger on the upper whorls, small and rather regularly arranged on the body whorl. A green nacreous layer inside aperture. Dimensions: height 10.5 mm; diameter 7 mm.

The type specimen is a sub-adult specimen of a species of Phasianotrochus. it is, as Thiele indicates, closest to P. rutilus (A. Adams, 1851) from Victoria and Tasmania. The only species seen by the writer from Cockburn Sound and its vicinity are P. bellulus (Dunker, 1845), P. apicinus (Menke, 1843), P. irisodontes (Quoy & Gaimard, 1834) and P. eximius (Perry, 1811). Phasianotrochus irisodontes is similar in shape and sculpture to C. sericinus but the examination of hundreds of specimens has shown that it always has a very characteristic colour pattern of fine red axial lines quite different from the essentially spiral arrangement of the brownish spots exhibited by Thiele’s specimen. Phasianotrochus apicinus has a much more sharply angled periphery than Thiele's specimen when it is the same size and also has fine reddish axial lines. Phasianotrochus bellulus is smooth and has a very distinct colour pattern and P. eximius has a more sharply angled periphery and distinct, rather widely spaced spiral grooves. Although the real status of C. sericinus will have to await further work it is possible that it represents a chance introduction of P. rutilus or a mislocalized specimen.

Cockburn Sound, Western Australia .