293 



ISOPYRE. 



ZULUS. 



294 



The same acute zoologist (loc. cit.) says that the Impoda, properly 

 so called, are Edriophthalmous Crustaceans, whose abdomen is never 

 rudimentary, and carries below five pair of false branchial feet, having 

 all nearly the same form and the same functions. The appendages of 

 the pet ultimate ring (or the false feet of the sixth pair) have a form 

 and use different from those of the preceding. The thorax, com- 

 posed in general of seven rings, but sometimes having only five, 

 carries nearly always seven pair of feet, which are often furnished 

 with a foliaceous palp, serving to protect the eggs and young, but 

 they hardly ever carry a vesicular appendage proper for respiration, 

 as in the Amphipoda and Lamodipoda. Finally, the conformation of 

 their buccal apparatus varies, and the greater part of authors are in 

 error when they assign to them as a character the possession of 

 mandibles deprived of palpiform appendages. 



M. Milne-Edwards is of opinion that the Jsopoda form three natural 

 families, namely, the Idoteidians, the Cymothoadians, and the Clopor- 

 tidians, and he thus distinguishes them : 



A. Jaw-feet operculiform, and deprived of a palpiform stem, or 

 only showing the vestiges of it. 



* Thoracic feet ambulatory ; last segment of the abdomen 

 smaller than the preceding segments ; internal antenna; 

 rudimentary. 

 These form the family of 



Cloportidians. 



* Thoracic feet anchor-like (anereuses), last segment of 

 the abdomen nearly always much larger than the 

 preceding segments ; internal antennae in general well 



These form the family of 



Cymothoadians. 



AA. Jaw-feet palpiform. Last abdominal ring much more 

 developed than the preceding ones; all or nearly all the 

 feet ambulatory. > 



These form the family of 



Idoteidiaus. 



In this classification, says the author, the family of the Clopor- 

 tidians has the same limits as in the method adopted by Lamarck, 

 and comprises the Terrestrial Isopods. 



The family of Cymothoadians is composed of the Parasitic Isopods, 

 and comprehends Cymothoa of Lamarck, lone, Anceut, and Typhis. 



The family of Idoteidians consists of Marine Isopods not parasitic, 

 and embraces the genera Idotea, Sphceroma, Anthura, Atellw, &c. 

 [CRUSTACEA.] 



Fotsil Isopoda. M. Latreille states that Professor Germar had sent 

 to M. le Comte Dejean the figure and description of a small Fossil 

 Crustacean which appeared to him (M. Latreille) to be referrible to 

 the sub-genus Limnoria; and he further remarks that Onitcut 

 pmguttator, figured in Parkinson's work, comes near to that species, 

 or at least appears to belong to the same section. 



M. Desmarest ('Hiatoire Naturelle des Crustacea Fossiles') enu- 

 merates two fossil species of the genus Sphteroma: one, S. antiqua, 

 found in a fragment of white fine-grained calcareous stone, analogous 

 in that respect to the Pappeheim stone, but of which he knows not 

 the origin : the other, .$'. Marc/arum, from the horizontal beds of green 

 fissile marl (marne verte fissile) at Moutmartre, above the gypseous 

 beds, mingled with Spirorbes. 



ISOPYKE, a Mineral which occurs amorphous in granite. The 

 fracture is flat and conchoidal. It is brittle, with a hardness of 5'5 to 6. 

 The colour is velvet- or grayish-black, occasionally dotted with red. 

 The colour of the streak is greeniah-gray. It slightly obeys the 

 magnet. Lustre vitreous ; opaque or slightly transculent. The 

 specific gravity is 2'9 to 3. It is with difficulty acted upon by acids, 

 and fuses before the blow-pipe. It occurs in the granite of St. Just, 

 near Penzance, in Cornwall. According to Turner's analysis, it 

 consists of 



Silica 47-09 



Alumina 13'91 



Lime 15-43 



Peroxide of Iron 20'07 



Oxide of Copper 1-94 



98-44 



ISO'TELUS, agenus of Fossil C'riutacea (Trilolitet) from the Silurian 

 strata, especially of North America. (Green.) 

 ISOTOMA. [LOBELIACEJ!.] 



ISPIDA. [HALCYONIDJS.] 



ISTIO'PHORI, a family of Bats. [CHEIROPTERA.] 



ISTIU'RUS, a genus of Saurians. [IUUANID.E.] 



ITABALLI. [VOCHYACE^.] 



ITACOLUMITE, a Micaceous Granular Quartz with wbicli gold 

 and topaz are associated. It is found in Brazil [DIAMOND.] 



ITCH-MITE, [ACARIDA] 



ITTNERITE. This Mineral occurs crystallised in rhombic dodeca- 

 hedrons and massive. It has a compact structure. The fracture 

 is imperfect, conchoidal, passing into uneven. Hardness 5'0 to 6'0. 



The colour is bluish or ash-gray. The lustre resinous to vitreous. 

 Specific gravity 2'3. It forms a jelly when put iiito acids, and fuses 

 per se before the blow-pipe, with effervescence of sulphurous acid, into 

 an opaque blebby glass. It yields by analysis 



Soda 11-29 



Potash 1-57 



Silica 30-17 



Alumina 28-40 



Lime g-24 



Oxide of Iron . . . . . . 0'62 



Sulphate of Lime . . . . 4'89 



Common Salt 1-62 



Sulphuretted Hydrogen and Water . 10'76 



94-56 



IU LUS, a genus established by Linnaeus for such Imecta Myriapoda. 

 as now form the order Chiloynatha (xeiAos, yvaBos), the first division 

 of Myriapoda in the arrangements of Leach and Latreille. The 

 Chilognatha have crustaceous and usually cylindrical bodies, formed 

 of numerous unequal segments, very short feet, each terminating in a 

 tingle hook ; a vertical rounded head, furnished with two mandibles, 

 which are either thick and robust or united with the labium and 

 elongated. They have no palpi. The antenna; are two, very short, 

 either subtly thickened towards their extremities, or filiform 

 throughout, and composed usually of seven, more rarely (as in the 

 genus Spharopceus) of six joints. Their ejes are smooth and vary 

 greatly in number. These animals move slowly and with a gliding 

 motion. When disturbed, they roll themselves up spirally, or into a 

 ball. They feed on decomposing animal and vegetable matter. 



The position assigned to the Chilognatha, at the head of the 

 Myriopoda, by Latreille and others, has been disputed by Professor 

 Brandt and by Mr. Newport. The following remarks on this subject 

 by the latter naturalist, of all living zoologists the most competent to 

 decide in questions affecting this difficult class, are taken from his 

 catalogue of Chilognatha in the British Museum, published in the 

 'Annals of Natural History for April, 1844,' and afford iu a brief 

 compass much information respecting theso curious animals. 



"The Chilognatha, have usually been regarded by naturalists as 

 the first order of Myriapoda, partly in consequence of the more 

 compact form of the head, and its similarity to that of the larva state 

 of hexapod insects, and partly from the general form of their bodies 

 being similar to that of the larva;. This was the view taken of these 

 animals by Latreille, Leach, Gervais, and some others, and very 

 recently by Lucas. But a different and, as I believe, more correct 

 view and arrangement have been followed by Professor Brandt, who 

 regards the Chilopoda as the first, and the Chilognatha as the second 

 division of the class. Although I cannot entirely agree with Brandt 

 in his division of the Chilognatha into masticating and sucking 

 species, because, as Lucas has recently remarked, there are species 

 even among the Chilopoda which have the external organs of nutrition 

 fitted only for taking liquid food, as in the little Scolopendrdla, I fully 

 agree with him in the superiority of the Chilopoda, as an order, over 

 the Chilognalha, notwithstanding the less compact structure of the 

 bead in the former. The general characters of the Chilopoda certainly 

 point them out as the most perfect animals of the osculant class of 

 Articulata. The more compact frame of body, the reduced number 

 of the organs of locomotion, the greater activity, and the preda- 

 ceous habits of the higher species, approximate tbe Chilopoda to the 

 predaceous insects on the one hand, and to the Arachnida on the 

 other. The form of the head, in the two divisions of Myriapoda, 

 seems to have reference chiefly to the particular habits of the species. 

 Thus, in those which seize their prey and subsist like the Arachuidaus 

 on living objects, those segments which in reality compose the whole 

 head are not all anchylosed together, but are in part freely moveable 

 on each other, and thus allow of a more preheusile function to the 

 large forcipated foot-jaws, the true mandibles of the Articulata. Some 

 naturalists have believed that these foot-jaws in the CIMopoda aru 

 not the true analogues of insects and of Chilognatha.; but I am 

 satisfied, by recent examinatious, that this is truly the case. In the 

 Chilognatha the foot-jaws have the form of true mandibles, because 

 the habits of the species require that compact form of the organ 

 which alone can be subservient, not to the seizing and piercing of 

 living prey, but to the grinding or comminuting of more or less solid 

 vegetable matter, on which most of the genera of Chilognatha entirely 

 subsist. In all other respects, both in their internal as well as their 

 external anatomy, and in their physiology and mode of growth, the 

 Chilognatha are decidedly inferior to the Chilopoda. They seem to 

 conduct us down to the Annelida from the vegetable-feeding Crustacea, 

 as the Chitopodado from the Arachnidaus to the same class." 



The Chilognathous Myriapoda are found in all parts of the world, 

 certain genera however affecting certain geographical divisions. Thus 

 the species of Glomeris are European ; those of Spiratlreptta and 

 Sph&ropceus African and eastern. The genus lulus, in its most limited 

 sense, includes European, Asiatic, and North American species. lulus 

 terratrii is a familiar British example. 



A synopsis of the genera of Clulognatha will be found in the third 

 part of the nineteenth volume of the ' Linnaean Transactions," 

 appended to a valuable memoir on the Myriapoda by Mr. Newport. 

 Professor Brandt's papers on these animals are published in the 



