Report on the zoological collections made in the Indo-Pacific Ocean ...

82 COLLECXIOJrs FROM MELANESIA.of the girdle. On parting the valves a feature is at once discoveredin the posterior one wliich enables us to distinguish the species :in this the margin is very much thickened within, of a dark browncolour, smooth, flattened, and destitute of teeth, whilst in C. spinigerthe latter are strongly developed and coarsely striated. The colourof the interior also differs : C. incaniis is stained with dark brown,the centre of the valves exhibiting a large defined black-brown markover the jugal sinus, the lamina) of insertion being whitish. Thecentral valves have a single, very small slit on each side, and thefront one has about nine : the former, with the exception of theseventh, are broadest across the posterior margin, as is also the casein the closely allied AYest-Indian C. piceus, whilst in 0. spinigerthe greatest diameter is across the laminae of insertion in front ofthe notch. The jvigal sinus appears to be rather deeper than in thehitter species. The specimens from IStewart Island, presented tothe British Museum by Mr. C. Traill, agree in allrespects with thisspecies ; the form, sculpture, and the insertion-plates are quite thesame.114. Chiton (SchizocMton) incisus.Chiton incisus, Soiverby, Pi'or. Zvol. Soc. 1841, p. Gl ;Reeve, Conch.Icon. fig. 43.Chiton elougatus, Reeve, I. c. figs. 40 a, b.Schizochitou incisus, Gray, Proc. Zoo/. Soc. 1847, p. 169 ; Shuttleworth,Bern. Mit.theil. 1853, p. G8 ;H. Sf A. Adams, Genera Rec.Moll. vol. i. p. 477, pi. 54. figs. 6, G a.Hah. Island of Zebu, Philippines {Cuming); Raines Island,Torz'es Straits (Lice) ; Clairmont and Bird Islands, N.E. Australia(Coppinger).The mantle is thick, of a somewhat spongy texture, alternately buffand dark brown, the latter colour falling opposite the middle of thevalves and forming interrupted irregular narrow stripes. The spinesupon it are very short, scattered, and of two colours, brown andwhite. The raised ridges, generally six in number on the terminalvalves, but sometimes varying to seven or eight, and two on thecentral ones, are remarkable in being studded with minute blackishbeads. The longitudinal fine ridges are peculiarly flat-topped,those on the central areas being straight, whilst on the lateral areasand the front valve they are wavy or zigzag. The lamina of insertionin the front valve is thin, externally striated, with six notchescorresponding to the radiating costa?. on the outer surface. In thecentral valves the lamina is considerably produced in front, with asingle small slit on each side : in the last valve it is thickenedposteriorly, interru])ted in the middle by a large sinus, is coarselystriated on the o,utside, and is slit in thiee or four places. The interiorof the valves is greenish, staiiicd with brown in the middle.