Shell of moderate size, 23 mm. (1 inch) in height, narrowly fusiform-biconic, with the spire a little less than height of aperture plus canal. Whorls 9, including a smooth subglobose protoconch of two whorls. Post-nuclear whorls firstly with a subsutural narrow fold sculptured with numerous short retractive laterally compressed nodes, followed by a smooth almost flat steeply descending shoulder area to a bluntly rounded tuberculate keel, which occupies the lower third of the whorl height. Tubercles about 15 per whorl, erect to slightly protractive, connected below by a single narrow spiral cord. Base with 4 or 5 rather distant spirals above, uppermost emergent from the subsutural fold, followed by gradually diminishing and more closely spaced spirals over the neck and anterior canal. Sinus of moderate depth, broadly arcuate, occupying most of the shoulder slope and confluent below with the considerable arcuately forwardly produced outer lip.

This species seems to have more in common with obtusigemmata than with the other two members of this group, in that the subsutural margining is crenulate rather than gemmate over the later whorls. Also the basal spirals are of uniform size, widely and evenly spaced in C.subsuturalis but in obtusigemmata there are two heavy upper basal spirals, followed by numerous weaker, more closely spaced cords.

Examination of the large series of John Murray Expedition- specimens revealed very a high variability of C. subsuturalis in sculpture and shell proportions. Some specimens are very similar to the original illustration of von Martens (e.g. Figs 37, 38) whilst others, often from the same station, may differ in narrower (or, conversely, broader) shells with more or less high position of peripheral keel, variously differentiated spiral ribs on the shell base, and more or less prominent and numerous tubercles on subsutural fold. The largest JME shell is 32.4 mm in height and 12.0 mm in width. Powell (1969, p. 285) mentioned 'a related new species from the Gulf of Aden in 1270 metres', i.e. from stn 184, but did not give a formal description nor reasons for this. However, extreme variants of C. subsuturalis from stn 184 are connected by intermediate forms and can be therefore identified as that species.
Specimens from two stations off Maldive Islands comprise a distinct group differing from East African shells in smaller size (15.5-21.0 mm at 6-7 teleoconch whorls vs. 21.8-28.7 in typical C. subsuturalis) and more slender shell proportions (H/D ratio is 2.82-3.12, mean 2.95 (n = 11) vs. 2.10-2.94 (2.10-2.70 in 19 out of 20 shells measured), mean 2.34). These differences are probably connected with geographical isolation of the Maldive Islands resulting in formation of morphologically isolated population of the species. If the above-mentioned metric differences will be confirmed in additional samples, the population of C. subsuturalis from Maldive Islands should be considered as a distinct subspecies. This population represents a transition (both geographical and conchological) to C. exstructa von Martens, 1903, described from Nicobar Islands. The latter species is distinguished only by an even narrower shell (H/D ratio is 3.43 in the holotype) with longer axial folds (as far as it can be judged from von Martens' figure). Examination of type material may however reveal that C. exstructa is a synonym of C. subsuturalis. A similar statement is probably true for C. obtusigemmata Schepman, 1913, which does not differ from C. subsuturalis in essential conchological characters.