Black dogfish to the clade formed by the granular dogfish ("C. granulatum") and combtooth dogfish ("C. nigrum"). The black dogfish is a common species, with a wide but discontinuous distribution in the temperate waters of the Atlantic Ocean; its range abuts, but does not extend into, the Arctic Ocean. In the northeast, it occurs from Iceland to Sierra Leone, including the Faroe Islands, southern Norway, and the Rockall Trough and Porcupine Seabight off Ireland. In the northwest, it is found from southern Greenland and Baffin Island to Virginia, being particularly abundant in the Laurentian Channel, and may occur further south to the
Rockall Basin (also known as the "Hatton Rockall Basin"). In 1956 the British scientist James Fisher referred to the island as "the most isolated small rock in the oceans of the world". The neighbouring Hasselwood Rock and several other pinnacles of the surrounding Helen's Reef are smaller, at half the size of Rockall or less, and equally remote, but those formations are legally not islands or points on land, as they are often submerged completely, only revealed momentarily above certain types of ocean surface waves. Rockall is about wide and long at its base and rises sheer to a height of