(®gure 19c)

Phyllidia xishaensis Lin, 1983: 153, pl. 1, ®gure 2.

Phyllidia varicosa: Bergh, 1905: 181, pl. 17, ®gure 8.

Phyllidiopsis striata: Wells and Bryce, 1993: 146; Brunckhorst, 1993: 69, pl. 8D±F.

Material. Chag96/6: 14 mm; outer reef, Ile Anglais, Salomon Atoll; 10 February 1996; at 12 m depth. Chag96/26: 18 mm; outer reef between Ile Boddam and Ile Poule, Salomon Atoll; 13 February 1996; at 8 m depth. Chag96/47: 12 mm; outer reef, Ile Diamante, Peros Banhos Atoll; 20 February 1996; at 23 m depth.

Description. Ground colour pale blue to white with four longitudinal black stripes, the inner two joining anteriorly between the rhinophores, the outer two joining anteriorly and posteriorly (®gure 19c). Black stripes separated by three pale blue to white ridges: the median ridge is simple, the outer two are doubled. Numerous small black spots present peripherally on the margin. Rhinophores lamellate, pale ochre in colour. Ventrally, the sole and the hyponotum are pale grey, and there is a black line on the hyponotum beneath the gills.

Geographic distribution. Indo-West Paci®c: from the Maldives and Seychelles (Yonow, unpublished) to Indonesia (Bergh, 1889), China (Lin, 1983) and the Marshal l Islands (Brunckhorst, 1993).

Remarks. This distinctive species is widely known as `Phyllidiopsis ’ striata; however, Phyllidiella striata (Bergh, 1889) is a species quite distinct from Phyllidiopsis xishaensis, and is also present in this collection from Chagos (see above). Phyllidiopsis xishaensis was ®rst described and illustrated by Bergh (1905: 181) but not recognized as a new species; he described a tiny specimen (9 mm) with`black behind the gills’ (trans.) from Siau Island (Indonesia) as Phyllidia varicosa Lamarck although`the foot sole is greyish white’ (trans.): P. varicosa has a black line on the sole. The ®gure of this specimen (Bergh, 1905: pl. 17, ®gure 8) is identical to the ®gure of a new species described by Lin (1983) as Phyllidia xishaensis. As Lin was describing an old preserved specimen (collected in 1958), the rhinophores, described as grey, had probably lost their ochre colour. The external pattern of this species is unmistakable (see Brunckhorst, 1993 and photographs in Wells and Bryce, 1993 and Coleman, 1989) and, since Phyllidiella striata and Phyllidia varicosa are misidenti®cations, the ®rst available name is Phyllidiopsis xishaensis. This is the ®rst record for the Indian Ocean.