ARTICULATA. Ill 



Order 6. Xiphosura. This order is here restricted to the single genus 

 Limulus {pi. 78, ßg. 34), which I^urmeister makes a tribe, under the name 

 of Poecilojjoda^ a name which has a very different value assigned to it by 

 other authors. On this account we prefer the name given by Gronovius. 

 The terms Episoa and Parisita are also used in such a manner as to cause 

 confusion, being applied both to the Lernmidoi and to the Anojplura or lice. 

 Limulus is remarkable for the long, hard, and sharp caudal spine, with 

 which spears are pointed in some countries. They are called king-crab on 

 the coast of the United States, where they are collected as food for hogs, 

 although these animals will not attack them until accustomed to such an 

 unusual kind of food. The body is covered by a large anterior carapace, 

 and a smaller posterior one, the gill feet are attached to the abdomen, and 

 six pairs of strong articulated ambulatory feet to the thorax. The latterare 

 present in the fossil species which have been discovered. The caudal stylet 

 is wanting in the embryonic young, which differs froui the adult in some 

 other particulars. The species live upon animal food. 



Malacostraca. 



Order 6. Isopoda. In this order the body is depressed and oval, and 

 there are seven pairs of feet attached to the seven movable segments of 

 nearly equal size which form the thorax {pi. 78, figs. 20-22). The young 

 resemble the adult, but they have only six pairs of walking feet. Some 

 of the species are parasitic upon fishes or Crustacea, and these have the 

 organs of motion and the eyes rudimentary. Most of the species are marine, 

 although some inhabit the fresh waters, and others the land, the last requiring 

 damp localities to preserve their gills from desiccation. The four antennae 

 are of a medium size, and directed in front, the first pair being in some 

 cases rudimentary. The organs of manducation are well developed, the 

 thorax occupies a great part of the body, the feet are armed with a single 

 nail, and in some cases they are prehensile. The females have a corneous 

 horizontal plate at the base of the feet, which forms a receptacle in which 

 the eggs are hatched. The abdomen is in the form of a terminal plate 

 above, and beneath it supports six pairs of organs, five of which are 

 respiratory false feet, and the sixth takes various forms, according to the 

 family. 



Milne Edwards divides the order into three sections, according to their 

 walking., swinwiing, and sedentary habits. The first includes the Idoteidce., 

 Asellidm, and Oniscidce / the second the Sphceromidce and Cg?>ioth&id(ß, 

 under a different mode of division from that of Latreille ; and the third the 

 Epicarides or Bopyridce^ under two families. 



The walking Isopoda have the terminal false feet in the shape of 

 operculums, or of projecting caudal stylets, which are never flattened into 

 swimming organs ; the first pair of antennjB are generally short or rud imentary . 



In the swimming Isopoda there is a large caudal fin provided with lateral 

 expansions formed by the modified fourth pair of false feet. All the antennae 

 have the same form, and the second pair are well developed. 



The sedentary Isopoda are parasitic, and whilst the males present the 



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