I found but one nest of the cork type at Montpellier, where it was most abundant, and invariably inhabited by the same spider, so that there can be little doubt that this is the celebrated _Nemesia cæmentaria_ of Latreille, the nests of which were described by the Abbé Sauvages in 1763. When living, the pattern on the abdomen is far more distinct and is traced on a paler ground than in _N. Moggridgii_, and the patterns on the back of the caput, as seen in specimens preserved in spirits, and the relative sizes of the lateral eyes, as well as other details enumerated by Mr. Pickard-Cambridge, afford characters by which they may be known apart; and it is probable that when the males, which are at present unknown, shall be discovered, they will be found to present other distinctive peculiarities. In the present instance we have the reverse of the case described above, in which two very distinct spiders constructed a similar nest, for here both spiders and nests are much alike. We have yet to learn what are the special advantages which each type of nest affords; but it is plain from the fact of the same type being adopted indifferently by both nearly- and most distantly-related spiders, that the form of the nest is governed far more by the conditions which it is contrived to meet, than by the affinity or resemblance of the spiders which construct it. I have found _N. Moggridgii_ at San Remo, Mentone, Cannes, Hyères, and Marseilles, but thus far, I only know of the true _N. cæmentaria_ at Montpellier. The latter spider is rather bolder than the former, and I frequently saw it at Montpellier watching at the slightly raised door, with the tips of the claws projecting from the nest, and it rarely failed to resist most vigorously any attempt of mine to force the door open. During the summer of 1873, I received two specimens of trap-door nests from California. Both of these nests were of the cork type and nearly entire, wanting only a small portion of the base of the tube; they most closely resembled one another and were probably the work of the same spider. For one of these, coming from the San Joaquin valley, between the Calaveras and the Tejon, I have to thank M. J. C. Puls, a Belgian entomologist residing at Ghent; and for the other, containing the spider which had constructed it _alive within its tube_ (!), I am indebted to Mr. G. H. Treadwell of San Francisco. The former nest is drawn at fig. A, Plate XV., and the spider[134] from the latter at fig. B of the same plate. [Footnote 134: This spider, which proves to be a new species, is described below (p. 260) as _Cteniza Californica_.] [Illustration: _Plate XV._] Mr. Treadwell had carried this spider and its nest, with the block of earth in which it lay, all the way from Visalia, a town about 350 miles south of San Francisco, where he had taken it; the nest and spider travelled safe to London enclosed in an empty cocoatina tin, 4-1/2 inches deep, and 2-3/4 across.