Victoria. Portland. Fully adult specimens are easily recognized by the dorsal pattern, which consists of a pale milky layer densely covered by hundreds of small brown specks. On immature and worn shells, where these characters are not present, dorsal bands somewhat similar to those of comptoni are visible, declivis differs from comptoni by its general colour being sepia rather than reddish brown, and by the more prominent pairs of terminal patches, the rear pair of which is the larger.
The close relationship between the two species is shown by some similarity in the fossular arrangement, though the teeth of declivis do not usually pvtpnrl sn far into the shell, and the fossular depression is less noticeable.