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valve for the attachment of the 

 cartilage externally. 

 TRIGO'NIA. \ (from Tpi^wvov, triangu- 

 TRI'GON. lar, Gr.) A genus of 



TEY'GON. ) marine bivalves, found 

 both fossil and living, belonging to 

 the family Ostracea. The trigonia 

 is a triangular or suborbicular, in- 

 equilateral, equivalve, transverse 

 bivalve. One valve has two oblong, 

 flat, diverging, hinge teeth, trans- 

 versely grooved on each side ; the 

 other "has four flat, oblong, di- 

 verging, hinge teeth, transversely 

 grooved on one side only, disposed 

 in pairs, receiving between their 

 grooved sides the two hinge teeth 

 of the opposite valve. Eecent 

 trigoniae have hitherto been dis- 

 covered near Australia only, in 

 sandy mud. They are nearly 

 related to the cardium, or cockle, 

 the foot of the animal being bent, 

 like that of the cockle, at an acute 

 angle, so as, upon pressure, to form 

 a very elastic organ. 

 TRILO'BATE. (from ires, three, and 

 lobus, a lobe, Lat.) Divided into 

 three lobes ; having three lobes. 

 TEI'LOBITE. (So named from its 

 being divided into three lobes or 

 principal parts.) A family of fossil 

 marine crustaceans, which appear 

 to have become extinct at the close 

 of the period during which the 

 carboniferous series was formed, 

 no traces of their remains having 

 been discovered in any strata of a 

 more recent period. For a long 

 time, fossil trilobites were con- 

 founded with insects, under the 

 name of Entomolithus paradoxus : 

 several names have also been given 

 to them, derived chiefly from the 

 three lobular divisions, by which 

 they are so characteristically mark- 

 ed, as well as from their being found 

 sometimes in a coiled, sometimes 

 in an extended state. By Bromel, 

 the trilobite was named Lapis in- 

 sectiferus; by Wolsterdorf, Con- 

 ehitus trilobus; by Hermann, 



Pectunculites trilobus imbricatus ; 

 by Da Costa, Pediculus marinus; 

 by LinnaBus, Entomolithes para- 

 doxus ; by Baumur, Trigonella 

 striata; and by Wilke, Entomo- 

 lithus cancriformis marini. The 

 trilobite is often called the Dudley 

 fossil, from its having been first 

 noticed in the transition limestone 

 near that town. "The great 

 extent to which trilobites are dis- 

 tributed over the surface of the 

 globe, and their numerical abun- 

 dance in the places where they 

 have been discovered, are remark- 

 able features in their history. 

 They have been found throughout 

 all northern Europe, and in nu- 

 merous localities in Worth America, 

 in the Andes, and at the Cape of 

 Good Hope. The anterior segment 

 of the trilobites is composed of a 

 large semi- circular, or crescent- 

 shaped shield, succeeded by a body 

 composed of numerous segments 

 folding over each other, like those 

 in the tail of a lobster, and gene- 

 rally divided by two longitudinal 

 furrows into three ranges of lobes. 

 The nearest approach among living 

 animals to the external form of 

 trilobites is that afforded by the 

 genus Serolis, in the class Crus- 

 tacea." 



TRILO'CTJLAR. (from tres, three, and 

 loculus, a partition, Lat.) A term 

 applied in botany to seed-vessels 

 divided into three portions or cells. 



TRINU'CLETJS. The name given by 

 Lhwyd to a genus of trilobites 

 found in the Caradoc sandstone and 

 Llandeilo Elags. 



TRI'ONTX. (trionices, pi.) A sub- 

 genus of fresh water testudo, be- 

 longing to the order Chelonia. 

 The soft-shelled tortoise. Several 

 species are mentioned. The soft- 

 shelled tortoises have no scales, the 

 shell and sternum being merely 

 enveloped in a soft skin ; many of 

 the pieces that are bony in the 

 tortoise being replaced by a simple 



