Marine geophysical data are used to interpret the continental margin structure south of India and west of Sri Lanka in the northern Central Indian Basin. Free-air and isostatic anomaly maps are presented. They show the prominent Indian Ocean gravity low with values more negative than -100 mgal south-west of Sri Lanka. A steep gradient in the free-air and isostatic anomaly forms a NNW-SSE trending line extending south and striking parallel to the southwest coast of India. This line marks the eastern boundary of a topographic and basement high here named the 'Comorin Ridge' which is also clearly seen on a sediment isopach map. The ridge seems to acto as a barrier to the passage of Ganges Cone sediments to the west. A comparison of the eastern (landward) edge of the Comorin Ridge with similar structures of other passive continental margins such as those off southe southern South Africa (Agulhas Fracture zone), off the Falkland Plateau and off western Norway is made. It is suggested that the eastern edge of the Comorin Ridge may mark a significant structural crustal boundary.