228 PERCY SLADEN TRUST EXPEDITION. 
58. Pseudoplesiops typus, Blkr. 
The first example of this monotypic genus to reach the British Museum was taken at 
Diamant at a depth of 16 fathoms, and shows that only the first ray of the dorsal and 
anal fins is a true spine, which is followed in each case by a number of simple articulated 
rays. Each ventral fin is made up of a slender spine and 4 simple articulated rays. 
The genus appears to be allied to Psewdochromis and to Plesiops. 
Chagos Achipelago, Peros, off Diamant Island. 
Centrarchide. 
59. Kuhlia teniura, C. & V. 
Seychelles Group, Praslin. 
Mullide. 
60. Upeneoides tragula, Richards. 
Maldives, Mulaku, 27 fathoms. 
Cheetodontida. 
61. Holacanthus somervillii, sp.n. (Plate 24. fig. 6.) 
Depth of body 2 in the length, length of head 3}. Snout ? as long as eye, the 
diameter of which is 2% in the length of head and equal to the interorbital width. 
Preorbital denticulated ; preeopercular spine } the length of head; no spines on lower 
limb of preeoperculum or on interoperculum. 50 scales in a longitudinal series. Dorsal 
XIV 16; spines increasing in length throughout ; length of base of soft-rayed part 13 
in that of the spinous part. Anal III 17. Soft dorsal and anal obtusely pointed. 
Caudal rounded. Pectoral nearly as long as the head ; ventrals extending to the origin 
of anal. Dark brownish; a large blackish humeral spot; body with several irregular 
narrow dark transverse bars directed somewhat obliquely downwards and forwards, 
each occupying the whole width of a transverse series of scales, but changing in its 
course from one series to another ; fins blackish, the caudal with a narrow pale edge. 
Seychelles Group, Coetivy. 
A single specimen, 64 mm. in total length. 
Closely allied to H. multispinis, Gthr. & Playf., which has 2 preopercular spines, 
the upper 4 the length of head, and 3 or 4 interopercular spines. 
Named after Comm. Boyle T. Somerville, R.N., who commanded H.M.S. Sealark 
during the expedition. 
Acanthuride. 
62. Acanthurus triostegus, Bl. 
Seychelles Group, Coetivy. 
Pomacentridz. 
63. Dascyllus nigripinnis, sp.n. (Plate 24. fig. 5.) 
Depth of body 1% in the length, length of head 33. Snout shorter than eye, the 
diameter of which is 2? in the length of head and equal to the interorbital width. 
