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

88 COLLECTIONS FROM MELANESIA.mouth and for a short distance along the sides, and then simple andgradually increasing in the width of the expansion towards theend, where it is very wide beneath the brauchia ; it is stained withblack on the inside of the edge. Branchial plume posterior, concealedbetween the foot and the hinder lobes of the dorsal disk. Headpresenting exteriorly a small lobe on each side the oral opening.Shell internal, situated at the hinder extremity above the branchia,white, calcareous, uncoiled, consisting of one or two volutions,thickened at the free " sutural line," convex externally and concavewithin, cup-shaped at the commencement, with the outer edgeextended by a broadish membranous expansion.Total length 33 millim. ; cephalic disk 18 long and 16 wide atthe broadest part ; shell with a greatest diameter of 8 millim., andabout 2 in height.Hah. Thursday Island, Torres Straits, 4-5 fathoms, on a sandybottom.The only species which appears to have been recorded from theAustralian coasts is Ar/laia lineolata, figured by H. & A. Adams inthe Genera of Eecent Mollusca,' ' vol. iii. pi. 58. fig. 4. This differs,however, in the form of the anterior dorsal disk and its smallsize in proportion to the hind part of the animal, in addition towhich the colour and markings appear to be quite distinct. AglaiagiglioUi, from Japan, described by Tapparone-Canefri (Voj*. Magenta,p. 110, pi. l.fig. 18), may be distinguished by the posterior lobationof the cephalic disk, different colour, and apparent different positionof the branchial plume.Doridium ct/aneum, D. nir/riim, and D. guttatum, described by Dr.Von Martens from the Indian Ocean, have not yet been figured.Until all these exotic species have either been compared or muchmore amply described and illustrated, there will remain much uncertaintyrespecting the identification of all or any one of them.126. Pleurohranchus angasi. (Plate VI. figs. K, K 1.)Animal (in spirit) uniformly pale buff, elongate ovate. Mantleprobably smooth in life, wrinkled by contraction, not very widelyproduced at the free margin. Foot broad, tapering behind, roundlysubtruncate in front, where there is a thickening forming a doublemargin beneath the proboscis. The frontal veil is straight in front,angular at the sides, which are grooved. Tentacles shortish, slit atthe outer side, with the minute eye-specks at their base behind.Branchial plume consisting of about sixteen leaflets. Penis spinelike,very acute, and slightly curved at the tip.Shell placed well forward, the pale apex being posterior. It isbrowii in front, glossy, and beautifully iridescent on the exterior.It consists of about a whorl and a half, the nucleus being spiral andhollow within. The last whorl is much prolonged by additionalstrongly defined concentric layers, and also ornamented with fineyet distinct transverse striae. The columella is arcuate, and has anumbilical groove parallel with it.