I wish to take the present opportunity of thanking Prof. Westwood for having afforded me special facilities for examining this and other specimens forming part of the very valuable collections under his care at Oxford.] These nests were forwarded with their living occupants (_Cteniza [Actinopus] ædificatorius_) from Tangiers to Prof. Westwood, who describes the nests as being "about four inches deep, slightly curved within, about three quarters of an inch in diameter, the valve at the mouth not being circular, but rather of an oval form, one side where the hinge is placed being straighter than the other. The valve is formed of a number of layers of coarse silk, in the upper layers of which are imbedded particles of the earth, so as to give the cover the exact appearance of the surrounding soil, the several successive layers causing it, when more closely inspected, to resemble a small flattened oyster-shell." The resemblance between this nest and that of the West Indian species is the more interesting as Prof. Westwood says that both belong to the same genus, (_Cteniza_ or _Actinopus_ of different authors,) and are so closely allied as to present scarcely any important distinction but that of size. We shall find, however, on comparing the nests of these trap-door spiders and their occupants, that we cannot as yet make any rule as to the kind of nest which we may expect from a given spider. It will be seen that species belonging to the same genus, and closely resembling one another, sometimes build dissimilar nests; while others, belonging to different genera, and unlike in many important respects, construct almost identical nests. This is the more strange, because, if we examine the structure of the claws and palpi, they often seem to be specially adapted to serve as carding instruments and to play a very important part in the weaving of the silk linings of the nest; and yet nests of the same type are occasionally produced by spiders in which these appendages are quite unlike, and dissimilar nests where the claws and palpi are to all appearance identical. Thus, for example, if the reader will examine the drawings of part of the foremost right foot of _Cteniza fodiens_, figs. A, 9 and 10, Plate VII., p. 88, with that of _Nemesia cæmentaria_, figs. A, 9 and 10, Plate VIII., p. 94, both of which make nests of the cork type, he will see that in the former the last joint of the tarsus is armed along the inner side, with many moveable spines, and that each of the two curved terminal claws has only one very strong tooth near the base; while the same joint of the latter (_N. cæmentaria_) has no spines, and the claws have three minute comb-like teeth near the base.