Shell small to moderately small. The profile is conical or ventricosely conical, with a low to moderate spire and a rounded shoulder. Outline of the last whorl straight or most often convex, rather concave abapically resulting in a slightly pyriform shape. The spire is almost always eroded, outline concave in those specimens in which it is preserved. Teleoconch sutural ramps flat, with spiral grooves. Suture well-marked. Last whorl smooth, with variably spaced fine spiral ribs present in the basal quarter. Aperture narrow, wider towards the base. The shell has a very dark brown color, almost black in ocassions, which appears lighter ventrally. Very fine characteristic dark brown, equally spaced spiral lines are usually visible, specially on the ventral side and in young specimens. There is a white spiral band around the middle portion of the last whorl which is covered by a dark brown reticulated pattern. The region between the shoulder and the midbody band displays often a fine reticulated pattern of white dots, although in many occasions it appears solid dark brown. The basal third is usually void of any reticulated pattern, being dark brown. On the shoulder there is often present a fine spiral band of a lighter brown color. Just above the shoulder and in the late sutural ramps of the spire, the reticulated pattern is replaced by irregular dark brown blotches on white. The upper part of the spire appears white due to erosion in most cases. The colour of the aperture is white in the larger specimens. In smaller specimens, the aperture is stained with purple-brown, with the inner lip white, and two white bands, one near the shoulder and another below the midbody. The aperture is white within. The columella is white.
Morphometric parameters: L = 18-31 mm; average L = 24.4 mm; RD = 0.62 -0.71; RSH = 0.07 -0.17; PMD = 0.81- 0.87.

C. vulcanus n. sp. resembles at first glance a very dark form of C. delanoyae Trovao, 1979. In fact, shells of C. vulcanus might have been circulating as C. cf. delanoyae. Despite the similarities between the shells of C. vulcanus and the shells of certain forms of C. delanoyae, i. e. dark specimens from Baia de Santo Antao, Derrubado , there are a number of features that allow their separation. Shells of C. vulcanus are very dark brown, almost black ocassionally, with a reticulated pattern most often reduced to the spiral band in the midbody of the last whorl. The fine spiral lines present, specially visible on the ventral side, as well as the lighter band around the shoulder are quite distinctive. On the other hand, the morphology of the robust radular tooth of C. vulcanus readily separates this species from C. delanoyae, which has a narrow and elongated radular tooth with apical portion longer than the basal portion. The radular tooth of C. vulcanus is very similar to the tooth of C. borgesi Trovao, 1979. However, the general aspect of the shells of C. borgesi and of C. vulcanus, which live sympatrically in Porto Ferreira, is quite different. C. delanoyae has also been found living sympatrically with C. vulcanus in certain localities, such as Baia das Gatas and Derrubado. The pattern of fine spiral lines present in young specimens of C. vulcanus gives them an aspect similar to that of C. crotchii Reeve, 1849, which lives in the opposite side (SW coast) of Boavista Island. However, adult shells of C. vulcanus are completely different to those of C. crotchii, their radular teeth being also different. Finally, certain dark forms of C. pseudocuneolus Rockel, Rolan & Monteiro, 1980 from Sal Island might also resemble C. vulcanus. Apart from the geographical separation, C. pseudocuneolus has a different radular tooth and lacks spiral lines in its pattern.

TYPE LOCALITY
Porto Ferreira, East coast of Boavista, Cape Verde Is.
DISTRIBUTION AND HABITAT
The highest density of specimens corresponds to the type locality. However, specimens have been found also in Baia das Gatas and in Derrubado, extending the range of this species to the north of Boavista. In Porto Ferreira, specimens were found on rocky reef, on large rock platforms usually covered with algae and some sand, between 1 and 3 m depth. Very often found in crevices and in empty sea urchin pocket holes on rock platforms. The same habitat has been observed in other localities (Gatas and Derrubado).