Page:VCH Rutland 1.djvu/83

 CRUSTACEANS purely inland counties, so in this, Asellus aquaticus, Linn., is the abundant but only fresh-water isopod to be found. It was taken in a disused canal and elsewhere near Oakham. The flattened dorsal surface is handsomely variegated with shades of brown. In front its two pairs of antennae are conspicuous, this twofold feature distinguishing crustaceans in general from insects, which have but one pair. Behind, the uropods or tail-feet are in like manner well calculated to attract attention, were it not that these appendages of the sixth pleon segment are in this species very likely to be broken off. In Asellus the segments of the pleon are fused dorsally into a shield, comparable with that fusion of anterior segments which throughout the Malacostraca and some orders of the other sub-classes produces the so-called carapace. In the terrestrial Isopoda, the wood-shrimps or garden crustaceans, as they have a right to be called, the pleon is in six compartments, fusion occurring only between the sixth segment and the telson. The species of this tribe found in the neighbourhood of Oakham were collected chiefly by Mrs. T. R. R. Stebbing, F.L.S., and proved to include the following species. In the family Oniscidae the ever-abundant Oniscus au/lus, Linn., was present in fields and at road- sides, and Philoscia muscorum (Scopoli) occurred in similar situations. These two species agree in having the flagellum or terminal lash of the second antennae three-jointed, but are easily distinguished by various other characters. The Oniscus has projecting front corners to the head, the dorsal surface tuberculate, the sides of the pleon continuing the curves of the middle body, whereas the much narrower Philoscia has the front of the head smoothly convex, a shining dorsal surface, and the pleon abruptly narrower than the middle body. PorcelHo scaber, Latreille, was taken under stones and timber in some profusion. In this species the two-jointed flagellum of the second antennae has the first joint a little shorter than the second or subequal to it ; the telsonic segment is a little hollowed dorsally, and has an acute apex. The normal colour is grey black, and the dorsal surface is rather densely granular. As is not uncommon, however, variously coloured specimens were met with, mottled or uniformly light brown, raising an expectation of distinct species, which on close examination was not grati- fied. Nevertheless, one specimen deserves more particular notice, as in addition to the mottled colouring and a very slender body, the first joint of the flagellum in the second antennae is only half as long as the second, and the short telsonic segment is rather obtuse at the apex. This combination of characters does not well fit any of our hitherto recognized British species. On the road between Oakham and Burley several specimens of Porallio pictus, Brandt and Ratzeburg, were procured. In this species the head and the central part of the pleon are black, the body is elegantly marbled, generally with a more or less linear arrangement of the dark and light portions. The second antennae are yellow at the base, and have the first joint of the flagellum longer than the second. Meto- ponorthus pruinosus (Brandt) was obtained among rotten hay in a field where a haystack had stood, and also at the edge of a flower-border from a garden in Oakham. This nearly straight- fronted species has the first joint of the flagellum in the second antennae longer than the second, but is distinguished from species of PorcelHo by having the pleon abruptly narrower than the middle body. It is dusky in colour, rather narrow, with the dorsal surface only slightly granular. The family Armadillidiidae supplies here abundance of Armaclillidium vulgare (Latreille), not in all places quite so common as its specific name implies. From its habit of rolling itself up into a ball it is, if not the commonest, perhaps the most familiar mem- ber of this tribe. Several of the specimens found were large and of the usual dark colour. Among these one had its left antenna colourless and much smaller than that on the right. This was evidently an instance of regeneration, a process by which crustaceans are able to re- cover lost appendages, although it is pretty clear that restoration of an appendage to its original size and vigour is only attained after a succession of moults. Some specimens of ArmadilH- dium were so small and brightly coloured that they suggested the presence of A. pulchellum (Zencker). The expectation, however, was disappointed, as the characters proved to be those of A. vulgare. The central stripe down the back was not dark, but light with dark borders, and the black colouring on the seventh segment of the middle body, distinctive oi A. pulchel- lum, was not present. It may be worth mentioning that in the terrestrial isopods the first antennae are very small and difl'lcult to observe. Their actual presence is an additional guarantee, if such were needed, that these forest shrimps, though no longer aquatic, are still true crustaceans. The sub-class Entomostraca is divided into three important orders, Branchiopoda, Ostra- c6da, and Copdpoda. In the first, only the sub-order Clad6cera can as yet be definitely attributed to this county. From the waters round Oakham, marsh and brook and fish-ponds, the following species were obtained, all belonging to the extensive tribe Anomopoda of the 47