I R I S I X I A. 



splendid cabinet, the other in that of the late Earl of 

 Tankerville. 



IRIS i LimiH'its). A beautiful and very numerous 

 genus of herbaceous perennials, belonging to the class 

 and order Triandria monogynia of Linn&an botany, 

 and to the natural order to which it gives a title, viz. 

 Irideec ; one or other of the species are seen in every 

 cottage garden ; the generality being hardy, and 

 increase themselves spontaneously. Some of the 

 foreign sorts require the care of the florist, as the Per- 

 sian and all the bulbous-stemmed sorts. The French 

 national emblem, Fleur-de-lis, is found here. 



IRON. The most important varieties of this 

 mineral will be described under the general article 

 MINERALOGY. 



ISAT1S (Bauchin), a genus of herbaceous annuals 

 and biennials, natives of Europe, belonging to Cruci- 

 ftree. One of the species is found wild in England, 

 viz. the /. tinctoria, and cultivated as a dye, under the 

 name of woad. It was, before the introduction of 

 indigo, a plant of considerable commercial importance, 

 and extensively cultivated in Somersetshire, especially 

 about Glastonbury, which town received its name 

 from the Celtic word glas, signifying blue. The an- 

 cient Britons are said to have painted their bodies 

 with the blue colour obtained from this plant 



ISOCARDIUM (Lamarck; CHAMALOR, Lin- 

 naeus). The molluscs constituting this genus have 

 been separated from the genus Chama of Linnaeus, 

 and the genera Cypricardia and Corditu of La- 

 marck's first arrangement of conchology, not only on 

 account of the peculiar shape of the cardinal teeth, 

 which principally guided his classification, but also on 

 account of the singular and graceful curvature of the 

 umbones, which are spirally turned on either side each 

 valve in the form of what is called familiarly a fool's- 

 cap, from which is derived the trivial English name 

 of the type of this genus, and is found in the Euro- 

 pean Seas ; the others inhabit the China and Indian 

 Seas. The hocardia, first described by Moltke, was 

 a few years since of great rarity and price, but is now 

 within the reach of every collector's purse. The 

 general description 'of shells of this genus is its being 

 equivalve, heart-shaped, globose, the umbones distinct, 

 and spirally recurved to the side of each valve ; two 

 flat primary teeth, one of which is bent and inserted 

 under the umbo ; a lateral prolonged callosity or 

 lengthened tooth ; and the ligament external and 

 forked on one side. De France enumerates six fossil 

 species, one of which is precisely analogous. 



ISOLEPIS (R. Brown). A genus of annual and 

 perennial grass-like plants, belonging to Cyperacece. 

 Common in British ditches and bogs, as well as iu 

 similar places in foreign parts. 



1SOPODA (Latreille). An order of crustaceous 

 insects belonging to the sub-class of Edrioplhulmous 

 mulacostraca, and embracing the Linnaeau genus GUIS- 

 CM, with the numerous sectional and generic s:r<>m>8 

 separated therefrom. It is distinguished by the hard 

 envelope of the body, the eyes not raised upon foot- 

 stalks, the body divided into a series of nearly equal 

 sized and generally flattened segments, and the legs 

 of nearly equal size, and fourteen in number, the ante- 

 rior pairs not being cheliferous, or armed with large 

 claws These characters ill readily distinguish them 

 Irom the leaping shrimps (Gammari", &c., order Amphi- 

 poda), and from the order L&modipoda, as well as 

 Iroin the great division of Podvpthalmous Crustacea. 

 Ihe leys are terminated by a short curved hook or 



nail ; he under surface of the abdominal portion of 

 the body is furnished with flattened appendages or 

 plates, having the edges fringed with fine hairs-, serv- 

 ing, as is supposed, for respiratory organs, and covered 

 by a larger pair. The body is generally flattened 

 and of an oval form, being broader than it is thick. 

 The internal pair of antennae are almost obsolete in 

 some of the most aberrant species of the order which 

 are not aquatic. The females carry their eggs for a 

 considerable period in a membranous bag, under the 

 breast or between the pectoral scales. The young 

 when hatched are very similar in form to their parents, 

 and undergo scarcely any other change than that of 

 an increase of size produced by the occasional shed- 

 ding of the outer envelope of the body. The greater 

 number of species inhabit the water, some of them 

 being parasitic upon fishes. The terrestrial species 

 also require a certain degree of moisture, in order to 

 preserve their branchiae in a fit state for respiration. 

 Latreille divides this order into six sections as 

 follows : 



1. Epicarides destitute of eyes and antennae, legs 



unfitted for locomotion. This section com- 

 prises only a single genus, Bopyrus, Latreille, 

 which is often to be found under the shell of 

 the prawn. 



2. Cymothoidee four antennae terminated by a 



multi-articulate slender thread, fore legs gene- 

 rally furnished with strong hooks. These are 

 parasitic upon fishes. Genera, Scrolls, Cymo- 

 thoa, IchthyophUus, jEga, and many other 

 genera established by Dr. Leach, including 

 the Limnoria terebrans, which is so destructive 

 in some of our ship yards. 



3. Sphteromidce antennas four, abdomen with two 



articulations, swimmerets composed of two 

 plates, the lower being moveable. Genera, 

 Zuzara, Sp/usroma, and other genera of Dr. 

 Leach. 



4. Idoteidee antennae four, placed on the same line, 



internal small, abdomen with three articulations, 

 destitute of lateral swimmerets. Genera, 

 Idotea, Stenosoma, Arcturus. 



5. Asellidce antennae four, inserted in two lines, 



abdomen composed of a single articulation, 

 without lateral swimmerets, and terminated by 

 two long and slender styles. Genera Ascllus, 

 Oniscoda, &c. 



6. Oniscida internal antennae almost obliterated, 



abdomen six-jointed with two or four terminal 

 appendages ; some are terrestrial. Genera, 

 Ligia, Oniscus, Porcellio, Armadillo. A figure 

 of the last named genus will be found in our 

 article CHILOGNATHA. 



ISOPOGON (R. Brown). A genus of evergreen 

 shrubs from New Holland, belonging to the class 

 Tetrandia and the natural order Proteacece. These 

 are ornamental plants, but require much care in keep- 

 ing healthy, owing to their being easily injured l>y too 

 much water at the root. They may be propagated 

 by cuttings, but with difficulty, if they get too damp. 

 IVY, a well-known British plant. See HEDERA. 

 1XIA (Linnaeus). A beautiful flowering genus of 

 Cape bulbs, belonging to the Iridece. The best soil 

 for the ixias, of which there are many splendid species, 

 is a mixture of sandy loam and leaf-mould, or moor- 

 earih. They require no water after they have done 

 flowering. They should be fresh potted in October, 

 and set in a cold frame well protected from frost. 



