shell (the wall not being represented in the diagram, but standing where the letter (_p_) stands), so it must be with the cement, which thus likewise comes, in an unusual manner, to invest the outer surface of the folded walls of the shell, and attaches them to the skin of the whale,--which latter is always growing upwards, and tending to bury the shell. _Platylepas decorata._--This genus is closely allied to Coronula, and the cementing apparatus is essentially similar. In one specimen, I counted no less than forty-nine slips of basal membrane, each of which, of course, had its pair of cement-glands, and each of the latter its two ducts. The glands consists of a transverse enlargement of the trunk, as in the early stages of Coronula. Neither the glands nor the duct, when old, become filled up with cement, but only the main-trunk. The ducts are very delicate and thin; the larger ones being only 3/10,000 of an inch in diameter. The glands stand some way apart on the two cement trunks; and the latter, instead of being straight as in Coronula, are deeply serpentine; the glands are formed on each bend, so that, though all on one side are connected on the same trunk, they form a double row on each side of the basal membrane. The basal membrane (in the centre of which I distinctly saw the antennæ of the pupa) has six deep bays or excisions, corresponding with the midribs (see Pl. 17, 1 _a_, 1 _d_) of the six compartments; and the two ducts from each gland, on the right and left sides, debouch at the heads of the four lateral excisions, exactly opposite the midribs of the lateral and carino-lateral compartments. The later-formed glands, owing to all of them being situated some way apart from each other on the two cement-trunks, lie further from the centre of the basis than do the orifices of their ducts; hence the later-formed ducts are directed a little backwards, or from near the circumference towards the heads of the deep excisions.