Diagnosis
Shell ovate-trigonal to trigonal, solid, smooth to glossy; umbones raised, slightly prosogyrate but markedly so in large adults; lunule elongate heart-shaped to lanceolate, flat, faintly delineated by incised line; anterodorsal margin short, widely rounded terminally; ventral margin widely convex; posterodorsal margin slightly convex, steeply sloping, narrowly rounded at termination. Sculpture of obscure concentric striae, well defined at anterior and posterior margins and stronger growth pauses. Colour externally white with brown blotches forming a dense network of fine chevron markings (tent shaped) over entire surface; umbones white, lunule white often with light-brown staining near umbones; shell internally white usually with yellow or pale orange medially. Dimensions of neotype: length 28.3 mm, height 26.2 mm, width of pv 18.5 mm. Shell length to 48 mm.

Distribution and habitat
Indo-West Pacific (including Japan (Habe, 1977)) in coral sand or loose sand and rubble, littoral to about 50 m. Australia: Queensland: trawled between Palm and Curacoa Islands, AMNH.303472 (7pv); trawled lagoon. Little Trunk Reef, AMNH.303471 (4pv); Slashers Reef no. 1, in lagoon, 10 m, AMNH.303284 (6pv); Lizard Island, AMNH.303283 (lpv). Papua New Guinea: 5-6 m,in sand around coral shoal, between Krankct Island and Madang, 5°12'S, 145°50'E, AMS C.356678 (5pv) (preserved); northern end Madang, 5°12'S, 145°51'E, AMS C.358000 (5 rv, 41v). New Britain: Duke of York Island, AMS C.68234 (lpv). Indonesia: Kalimantan, 14 km N of mouth of Mahakan R., KL (llv). Solomon Islands: Honiaro beach, AMNH.303374 (lpv). New Caledonia: Scctcur dc Koumac, 10-16 m, AMNH.303406-AMNH.303409 (4pv); Anse Vata, AMNH.303285 (lpv); Noumea, AMS C.86251 (many) (full New Caledonia locality data is provided Lamprell and Stanisic (1996)). New Hebrides: AMNH.303279 (lpv). Fiji: Nadi Bay, 34.5 m, AMS C.67589 (many). Philippine Islands: Tabangao, Batangas Prov, Luzon Island, AMS C. 104739 (1 pv); Sulu Sea, Cuyo Islands, AMS C.2228 (1 rv, 1 lv); Luzon Island, entrance to Manila Bay, Corrcgidor Island, AMS C. 138086 (lrv); Luzon Island, Bauang, Perez Beach, AMS C.141441 (lrv, llv); Palawan Island, N Hondo Bay, Tanabag Beach, AMS C.371091 (lrv). Mozambique-Northern Zululand (for full localities refer Lamprell and Kilburn (1999a), all NM material). Mauritius: AMS C.96966 (lpv). Red Sea: Dissal Island, off Massana, AMS, no number (3pv); NE of Safaga Town, among coral and sand, NMW Z. 1997.021.100 (lpv). Israel: Eilat, KL (6pv).

Remarks
Lamprell and Kilburn (1999a) established a neotype for this species from material in the Spengler Collection. This material is representative of what we may term 'typical' L. ornata. During the course of the present study, we have examined several specimens, especially from the south-western Pacific, which indicate to us that L. ornata (as broadly interpreted herein) either represents a complex of species, subspecies or geographic variants or, as recently suggested by Lamprell and Stanisic (1996), is simply an extremely variable species with the ability to generate a number of distinctive colour and/or morphological forms at any one locality. As indicated elsewhere in this paper, occasional specimens of L. ornata may show shape and/or pattern similarities to L. fastigiata and L. annettae and, by so doing, somewhat blur the boundaries between these three taxa. Unfortunately, examination of the hinge teeth from an extensive range of material has not yielded any characters to help separate these three species, leaving colour pattern, valve shape and sculpture as the only useful means of discrimination. Specimens from Israel often show a patch of purple internally and are trigonal, even in very juvenile specimens. A very attractive form from the Solomons and New Guinea exhibits minute rows of spots, which merge into fine zigzag markings near the dorsal edge. Specimens from the outer region of the Great Barrier Reef are large (45-48 mm), heavy, trigonal and exhibit minute tents in their patterning. The frequent occurrence of intermediates between several of the 'forms' suggests that they are all merely variants within a single species. However, it is hoped that future molecular and/or detailed anatomical work will assist in determining whether some of the more distinctive forms here grouped under the name L. ornata deserve to be recognised taxonomically.