CEMENTING APPARATUS. 143 



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. 



Tlatylepas decor ata. — This genus is closely allied to 

 Coronula, and the cementing apparatus is essentially simi- 

 lar. 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 -^ 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 antennae of the 

 pupa) has six deep bays or excisions, corresponding with the 

 midribs (see PL 17, la, I 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 com- 

 partments. 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. 



Tubicinella. — The cementing apparatus is here less sym- 

 metrical ; but this, I believe, is chiefly owing to the basal 

 membrane bemg formed of successively larger discs (not slips) 

 of membrane, thrown down not quite concentrically one 

 over the other ; each new disc of membrane seems to cover 

 the last-formed cement-glands and ducts; and there are 



