which, though adult, have not attained the maximum size, are represented, this descending cavity, though overlooked by me, should have been shown, for it must certainly have existed.
Its presence was first observed by the Honourable L. G. Dillon, who detected it when tracing the course of the main tube upwards from below. I had always followed the tube from above downwards, and in so doing must have unwittingly filled up the descending cavity (the existence of which I was far from suspecting) with detached particles of earth.
I will own that, when Mr. Dillon first showed me this new feature, I hoped that it might prove to be something accidental and exceptional; and it was only after careful examination of a large series of nests of all sizes, that I gradually and almost unwillingly admitted that this descending cavity formed an important feature in the typical structure of the nests.
I now see, however, that the presence of this cavity adds considerably to the interest of the structure as a whole, and places its architect quite at the head of all the builders of trap-door nests. This type should now be called, for the sake of distinction, the double-door, branched, cavity, wafer nest, to avoid confusion with the Hyères branched nest.
I am now about to endeavour to atone for my past oversight by giving new illustrations (Plate XIX., figs. A and B) and descriptions of this very remarkable nest; while I would at the same time beg the indulgence of my readers for past and present shortcomings, reminding them that the interest which attaches to structures of this kind is proportioned to the com-
