Accessory dorsal arm-plates present.

Disc-scaling coarse and compacted so that some scales are largely obscured by their neighbours: supplementary plates, short, mainly confined to sides of arm and not conspicuous from above. . . . Ophiodesmus Ziesenhenne, 1940.

*amphilogus Ziesenh., 1940. L. Calif. Littoral.

(A. M. Clark (1953) considers the second of these characters more distinctive.)

Disc-scaling relatively fine, the scales not especially compacted: supplementary plates conspicuous from above. . . . Ophionereis Lütken, 1859.

*Ophiura reticulata Say., 1825. Caribbean. Littoral.

For discussion of Ophionereis see A. M. Clark (1953). The following probably do not rank higher than subgenera of Ophionereis:—Ophiotriton Doederlein, 1896, lacking obvious scales on the disc: Ophiocrasis H. L. Clark, 1911, with 2 or more supplementary plates (as opposed to Ophionereis s.s., which supposedly has only 1 supplementary plate).

No accessory dorsal arm-plates.

In addition to the large tentacle-scale, one or two much smaller scales may occur, at least on the basal arm-segments.

Spines on disc, both above and below, and across the dorsal arm-base. Ophiodoris Koehler, 1904.

*malignus Koehler, 1904. Indonesia. 250 fms.

No spines on disc, but granules present on ventral interradii, and sometimes also above. . . . Ophioplax Lyman, 1875.

*ljungmani Lyman, 1875. Caribbean. 100 fms.

Only the large tentacle-scale present: Disc entirely free from spines or granules: arms keeled above and below. . . . Ophiochiton Lyman, 1878.

*fastigiatus Lyman, 1878. Japan. 100 fms.