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

—474 COLLECTIONS FROM MELANESIA.in the arm. is not quite constant in its position. The rest of thecharacters agree with those of the typical form.Hah. West Island, Torres Straits, 7 fms. ; bottom sand.Variations. This sponge varies, as has been seen, in shape (ovalor subspherical) and in the presence or absence of a vent. A thirdvariation may be noted, viz. in the length, stoutness, and amountof curve in the arms, and in stoutness of the shaft of the zonespicule; thus in a specimen from the Arafura Sea the diameter ofthe shaft falls to '045 millim., that of the arms to '043 millim., thelength of the arm remaining -25 millim., while the backward bend ofthe arm, though gradual, is very decided.The variations in this spicule, which is the only one which seemsto differ much in different specimens, are as follows :Diam. ofshaft.1. Port - Darwin specimen2. Thursday Island specimen3. Arafura -Sea specimen4. Var, retroflexa (WestIsland, Torres Straits)