No representatives of this family have hitherto been recorded from New Zealand waters. The familial characters include alternation in the position of the superomarginal and inferomarginal plates, and the restriction of the papulae to definite areas ("papularia") at or near the bases of the arms. The tube feet have a small sucking disc. As the name suggests, the family is essentially a deep water group. The genera occurring in New Zealand waters may be distinguished as follows:

An unpaired interradial marginal plate present	Benthopecten
No unpaired interradial marginal plate	Cheiraster

Benthopecten Verrill, 1884

Benthopecten pentacanthus sp. nov. Plate 1, Figs. D, E (holotype).

Diagnosis: Superomarginals each carrying two spines, one of which is enormously enlarged on each of the five unpaired interradial supermarginal plates. Abactinal intermediate plates each carrying one, or occasionally two similar, spinules. Inferomarginals each carrying one erect spine, plus one or two secondary spinules. The unpaired inferomarginal carrying three larger and two smaller spines. Adambulacral armature of three furrow spines and two subambulacral spines. Oral plates each with four furrow spines, the median one enlarged, plus two suboral spines.

Material Examined: Two specimens, both from the same locality, depth 400 fathoms, off Mayor Island, Bay of Plenty, Dom. Mus. Station B.S,210, 28/2/1957, R. K. Dell.

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Remarks: Both specimens are juvenile forms, as evidenced by their smaller size, and the fact that neither pedicellariae nor actinal intermediate plates arc developed. Benthopecten styracius Fisher, from Macassar Strait, would seem to be the species most closely related, and differences in the number of furrow spines (7–8 in B. styracius) and in the oral armature, could well be due merely to immaturity of the New Zealand material. However, Fisher expressly draws attention to the fact that B. styracius has only one spine on each supermarginal, whereas B. pentacanthus, despite its immaturity, already has two. Again, in styracius there are two inferomarginal spines, of which the uppermost is the longer, whereas in pentacanthus there are usually three inferomarginal spines, the lowermost being the largest. Another Pacific species, Benthopecten polyctenius Fisher, is somewhat similar, but lacks the five giant spines of the unpaired superomarginals.

Holotype: In the Dominion Museum, Wellington. R 5 mm, r 2 mm.

Cheiraster Studer, 1883

Cheiraster richardsoni sp. nov. Plate 1, Figs. F, H, holotype.

Diagnosis: Abactinal paxillae of both disc and arms having an enlarged central spine. Enlarged subcircular pectinate pedicellariae present on the abactinal surface, on the actinal intermediate areas, and occasionally also on the interbrachial marginal angle.

Description: Abactinal paxillae of disc and arms comprising 8–15 short spinules surrounding the central, enlarged vertical spine, in either a single or a double circle. Several enlarged pectinate pedicellariae on the abactinal surface of the disc (in the holotype there are three). Supermarginal plates forming a conspicuous border, each one broader than long, bearing a dense coat of erect spinules, and the interbrachial ones carry in addition a small erect spine occasionally. In the holotype there are 32 superomarginals in an interbrachial arc. from arm-tip to arm-tip. Inferomarginals broader than long proximally, but becoming longer than broad in the distal part of the arm. The proximal ones carry two (occasionally one or three) erect spines, on the outer surface, as well as the coating of erect spinules.

Actinal intermediate areas small, in the holotype not extending beyond the fourth adambulacral and second inferomarginal. Each intermediate plate bears one enlarged and several small spinules, except for the two interradial plates, which instead each carry five finger-like spines forming the comb of the pectinate pedicellaria. Adambulacral plates with a furrow prominence, bearing 6–8 furrow spines and 5–6 similar spines on the outer margin, together with one enlarged subambulacral spine. Oral plates each carrying about 9 furrow spines, the inner three much enlarged, especially the innermost one. The four suboral spines form a linear series on the actinal surface of the plate, the proximal one enlarged.

Material Examined: The unique holotype, from 400 fathoms, Cook Strait, VUZ Station 87.

Remarks. Cheiraster richardsoni falls in Fisher's grouping of species with an enlarged central paxillar spine, present on both disc and rays. From C. niasicus Ludwig it is distinguished by having pectinate pedicellariae on the abactinal surface, and from C. pilosus Alcock it differs still more, since there are apparently no pedicellariae at all in that species (see Fisher, 1919, p. 195). From C. inops it differs by having paxillae as numerous on the disc as on the arms, and by possessing pedicellariae. One other species, C. trullipes (Sladen) is comparable, as it has large subcircular actinal intermediate pectinate pedicellariae—however, C. trullipes falls in the grouping of species which lack the enlarged central paxillar spine.

Holotype: In the Department of Zoology, Victoria University of Wellington. R 31 mm, r 9 mm.