T B I 



[445] 



T B 



cartilage or membrane. Fossil 

 remains of trionices are found in 

 the fresh water Wealden formations 

 of the secondary series. Eemains 

 also are abundantly found in the 

 lacustrine deposits of the tertiary 

 formations. 



TBI'POLI. An admixture of silex 

 and clay. It has obtained its name 

 from having been originally brought 

 from Tripoli, in Barbary. It is a 

 mineral of a dull argillaceous ap- 

 pearance, occurring usually in 

 friable or earthy masses. Its 

 powder is fine, but dry and rough 

 to the touch, and sufficiently hard 

 to scratch metals, glass, &c. It is 

 employed for the polishing of 

 metals and stones. Kotten-stone 

 and polishing slate, the Polier- 

 chiefer of "Werner, appear to be 

 varieties of Tripoli. By recent 

 discoveries made by Prof. Ehrenberg 

 it is ascertained that tripoli is en- 

 tirely composed of millions of the 

 skeletons or cases of microspic ani- 

 malcules. At Eilin, in Bohemia 

 a stratum of tripoli extends over a 

 considerable space, being in some 

 parts fourteen feet thick. This 

 stone, when examined through a 

 powerful microscope, is found to 

 consist of the silicious cases of 

 infusoria united together without 

 any visible cement. From a cal- 

 culation made by Ehrenberg, it 

 would appear that in the Bilin 

 tripoli there are 41,000 millions of 

 individuals of the Gaillonella dis- 

 tans in every cubic inch. 



TBISE'PALOTTS. (from tres, three, and 

 sepal.) A term used in botany for 

 a calyx that has three sepals. 



TEI'TO^. A genus of the molluscous 

 order of Nudibranchiata, inhabiting 

 an oblong, thick, ribbed, or tuber- 

 culated spiral shell. The body is 

 oblong; mouth with an involute 

 spiral proboscis ; tentacula twelve, 

 six on either side, divided nearly 

 to the base, the hind one cheliferous. 



TBOCHI'TA. A detached vertebra of a 



radiated animal. When several 

 trochitse are united, so as to form 

 part of a column, the series is 

 termed an entrochite. 



TKOCHO'TOMA. A genus of fossil 

 trochiform univalves, distinguished 

 from Trochus and Pleurotomaria 

 by having a fissure upon the last 

 whorl, which approaches the outer 

 lip but does not reach it. Six 

 species have been procured in the 

 Great Oolite near Minchinhampton, 

 and four in the Inferior Oolite of 

 the same locality, one species is 

 likewise recorded from the Lias of 

 Normandy. Lycett. 



TEO'CHUS. (trochus, Lat. a top.) A 

 genus of conical, spiral, thick, stri- 

 ated, marine, univalves, found both 

 fossil and recent. Aperture trans- 

 versely depressed, and somewhat 

 quadrangular ; columella oblique ; 

 operculum horny, with numerous 

 whorls. Eecent trochi are found 

 in the ocean at depths varying to 

 forty-five fathoms ; they most com- 

 monly, however, are met with 

 near the shore, creeping on rock's, 

 sands, and gravel. One hundred 

 and thirty-three species are descri- 

 bed in Turton's Linne. Lamarck 

 has separated from the genus tro- 

 chus of Linnaeus certain shells 

 possessing peculiar characters, 

 which he has arranged under 

 two new genera, namely, Solarium 

 and Monodonta. These genera, as 

 well as trochus, are comprised in 

 the family Turbinacea. 



Very large casts of trochi are 

 found in Oxfordshire, Gloucester- 

 shire, and Sometshire. 



TRONGOTHE'EIUM. The name assigned 

 to an extinct species of beaver, 

 larger than any now known, whose 

 fossil remains have been found in 

 Eussia. 



TKOGONTHE'RIUM. An extinct fossil 

 genus of Eodents, nearly allied to, 

 but much exceeding in size, the 

 beaver. A relic of Trogontherium, 

 discovered by the Eev. Mr. Green, 



