The last species the _O. rufa_, that in which the female is remarkable for its inverted horns, which must be for some use in its economy, is perhaps the most common of all. I have found it in abundance upon old walls with a sunny aspect at Erith, and throughout the pleasant Crays of Kent. It is indifferent as to the choice of its domicile, selecting either walls, where I have chiefly found them, sandbanks, or the decaying stumps of pollard-willows. Its processes are similar to those of some of the earlier described, but its larva is longer in full feeding, which, when it has consumed all its provender spins a tough cocoon of brown silk, wherein it undergoes its changes; some, depending much upon locality, pass into pupæ in the autumn, others hibernate as larvæ which are subject to destruction from the attacks of the _Chalcideous_ insect, _Monodontomerus dentipes_, previously noticed under _Anthophora_. Some of the _Chrysididæ_ also infest several of the species of this genus, and I have no doubt that _Stelis aterrima_ is parasitical upon one of them, although it has not been recorded. The various species frequent many flowers, especially those abundant in the locality they inhabit, but the _O. pilicornis_ chiefly affects the common Bugle (_Ajuga reptans_), and they much frequent composite flowers, especially the species of the genus _Hieracium_. ------- Section 2. _Cenobites_ (_dwellers in community_). Subsection 1. SPURRED. † _Parasitical._ Genus 25. APATHUS, _Newman_. (Plate XIV. figs. 1 and 2.) APIS ** _e_ 2 partly, Kirby.—PSITHYRUS, St. Fargeau.