A HISTORY OF HERTFORDSHIRE less, slow-moving woodlouse left on the floor of the nest unfriended and alone. Porcellio scaber, Latreille, is nearly as long but not quite so broad as Oniscus asellus, from which it is distinguished by its granular roughness. It is even more common and more widely dispersed, and as a rule more sombrely dark, but it exhibits varieties in colour and markings. Metoponorthus pruinosus (Brandt) has 'the forehead straight,' a feature to which the Danish writer Budde-Lund alludes in the name he framed for its genus. In Oniscus and Porcellio and various other genera it will be found that the front line of the head displays a median lobe between two lateral horns or projections, but in Metoponorthus all this indenturing is flattened down and obscured. The present species is said by Budde- Lund to have the world for its fatherland, being a cosmopolitan that by navigation has wandered all over the globe. Cylisticus convexus (De Geer) is far from being familiar in England, although its distribution is probably extensive in our islands, as it certainly is in the north and middle of Europe. Unlike the other members of its family, this species has the capacity of rolling itself up into a ball, a defensive device that must puzzle and surprise many oppo- nents. The convexity of the body which makes this englobing of itself possible to the animal is noted in the specific name chosen by De Geer in 1778. But long afterwards Lereboullet, dealing with the same species in 1853, named it Porcellio armadilloides, thereby recognizing its family likeness to Porcellio and its specific or particular likeness to members of the family Armadillidiidae, to which the next species belongs. Armadillidium vu/gare (Latreille) shares perhaps with Oniscus asellus and Porcellio scaber the familiarity that breeds contempt, and in the competition for popular notice it surpasses both by reason of the habit just described, which it has in common with Cylisticus convexus. Here, however, the habit is not exceptional. It is characteristic of the family, that is to say, it belongs as a rule to all the genera and species, to have the body very convex and contractible into a globe. In concluding this interesting list of numerous species from a com- paratively small tract of ground, it should be mentioned that such a collection is not entirely without precedent elsewhere, that an old highly cultivated and diversified garden is a specially favourable territory, and lastly that, little esteemed as woodlice are among gardeners, they here evidently thrive and flourish without any serious detriment to fruit and flowers, and rather to the satisfaction than otherwise of the scientific horticulturist who is their overlord. 1 For Oniscus asellus, for Armadillidium vu/gare, for the freshwater 1 Annals and Magazine of Natural History, ser. 7, vol. iii. pp. 72-75 (1899). In this paper six of the species are expressly referred to Hertfordshire, while only general distribution is noted for Onitctu asellus, Philoscia muscorum, PorcelRo scaber, and Armadillidium vulgare. But I have in manuscript from Dr. Norman a list of all the ten as found in his garden, and while staying with him at Berkhamsted was able to observe almost all of them in their actual haunts, and in particular Haplofhthalmus danicus outside the greenhouse. 186
