The difference between S. contabulata and S. scalata mainly consists of a different development of the sutural area and of the umbilicus. It must be taken into account that the outline of the aperture peristome depends on the growth stage of the shell. If the last axial rib is not fully formed at the animal's death, the outer lip is thin and clearly shows the shape of the sutural area: flat, or excavated. When the last axial rib is fully formed, the peristome is thickened, and a solid tooth (sometimes bifid) is formed between the suture and the posterior notch at the shoulder. In apertural view, this structure can hide the exact shape of the sutural canal: an excavated sutural canal can be covered by a big tooth.The shells here identified as S. scalata have a tendency to have a double or triple spiral row of close-set nodules on the shoulder of the axial ribs ,forming a linear, abaxially descending row per axial rib. Lobbecke (1886: 74) remarked this on the shells he figured although this feature is hardly recognisable in his figures.
Locality: The species S. scalata and S. contabulata were described from "East Indies" and "Ceylon", respectively (Sowerby I, 1832). The shells discussed by Sowerby II (1849) and by Reeve (1856), and also C. articularis Sowerby I, 1832, were collected by dr Sibbald (Reeve writes "Dr. Siebold"), the head of the medical staff at Trincomalee in 1829 (Holman 1840: 293), in Ceylon; hence a reliable source for that locality).
Petit (1980: 213, fig. 4) figured S. contabulata and stated that it is readily separable from S. scalata by the latter's U-shaped sutural area, which is flat and sloping in S. contabulata. He stated that the two are "evidently closely related, but readily separable", and that S. scalata "appears to be restricted to Mauritius", but he gave no reference for that statement; while S. contabulata is "widely distributed". Baker (1891: 23) was the only one to report Cancellaria (Trigonostoma) scalata as "very common" in an unspecified large collection of fresh shells from Mauritius. Hemmen (2007: 280) stated: "Indeed S. scalata is a species - close to S. contabulata -occurring around Mauritius and in the Seychelles only". He added that he and two others had been snorkelling for 3 weeks in March-April 1976 all around Mauritius, and had not found a single shell of S. scalata. Perhaps these apparently contradictory statements might be related to a seasonal occurrence of the species in the shallow waters there.
Distribution: The shell of Cancellaria contabulata in the Lobbecke collection (ALMD) is from Ceylon; and his three shells of C. scalata are supposed to originate from Ceylon ("von wo die drei abgebildeten Exemplare meiner Sammhmg stammen sollen,f (Lobbecke, 1886: 73). Hence not Mauritius.