Chalicodoma, house of pebbles, rough-cast mortar, a name which would be perfect did it not look odd to any one not well up in Greek. It is a name applied to those Hymenoptera that build cells with materials such as we use for our dwellings. It is masonry, but made by a rustic workman, better used to dried clay than to hewn stone. A stranger to scientific classification (and this causes great obscurity in some of his memoirs), Réaumur called the worker after the work, and named our builders in dried clay Mason Bees, which paints them exactly. We have two kinds, C. muraria, whose history is admirably given by Réaumur, and C. sicula, which is not special to the land of Etna, as the name suggests, but is found in Greece, Algeria, and the Mediterranean region of France, especially in the department of Vaucluse, where in May it is one of the most common Hymenoptera. The two sexes of C. muraria are so unlike in colouring that a novice observing both coming out of the same nest would take them for strangers to one another. The female is of a splendid velvet black, with dark violet wings; in the male the black velvet is replaced by a bright iron-red fleece. The second species—a much smaller one—has not this difference of colour, both sexes wearing the same costume—a general mixture of brown, red, and ashy tints. Both begin to build in the beginning of May. The wing-tips, washed with violet on a bronze ground, faintly recall the rich purple of the first species. As Réaumur tells us, C. muraria in the northern provinces chooses as the place to fix her nest a wall well exposed to the sun and not plastered, as the plaster might come off and endanger her cells. She only entrusts her constructions to a solid foundation, such as a bare stone. I see that she is equally prudent in the south, but, for some reason unknown to me, she generally chooses some other base than the stone of a wall. A rolled pebble, often hardly larger than one’s fist,—one of those with which the waters of the glacial period covered the terraces of the Rhône valley,—is her favourite support. The great ease with which such a one is found may influence her; all our slightly raised plateaux, all our arid thyme-clad ground, are but heaped pebbles cemented with red earth. In the valleys the bee can also use the stones gathered in torrent beds; near Orange, for instance, her favourite spots are the alluviums of the Aygues, with their stretches of rolled boulders no longer visited by water. Or if a pebble be wanting, she will establish her nest on a boundary stone or an enclosing wall.