T E S 



[434] 



THE 



Crustacea it is phosphate of lime. 

 The testacea also retain their shells 

 as long as they live ; the Crustacea 

 cast them annually, or, at least, 

 periodically. 



TESTA'CEOUS. (testaceus, Lat. testacee, 

 Er. testaceo, It.) Belonging to the 

 the order Testacea ; having a strong 

 thick shell, the calcareous portion 

 of which consists of carbonate of 

 lime. 



TESTU'DINATE. (testudinatus, Lat.) 

 Arched ; vaulted j resembling the 

 back of a tortoise. 



TESTU'DO. (testudo, Lat.) 



1. A genus of the order Chelonia; 

 the tortoise. This genus has been 

 divided into five subgenera. 



2. The land tortoise, a sub-genus 

 of the genus above mentioned. 



TE'TRABRANCHIA'TA. The second order 

 of the class Cephalaphora, compri- 

 sing the nautilus, ammonite, &c. 



TETRACAU'LODOF. An extinct animal 

 of the order Mammalia ; allied to 

 the mastodon, and referrible to the 

 miocene period. 



TETRADA'CTYLOUS. (from TerpaSdicTv- 

 Xo?, Gr.) Having four toes. 



TETRADYNA'MIAIT. | A term applied to 



TETRADYNA'MOTJS. j plants that have 

 six stamens, four of which are 

 longer than the other two: the 

 wall -flower is a familiar example. 



TE'TRAGYN. In botany, a plant that 

 has four pistils. 



TETRAHE'DRAL. Having four triangles, 

 equal and equilateral. 



TETRAHE'DRON. | (from rerpa, four, 



TETRAC'DRON. j and etya, side, or 

 base, Gr. Utraedre, Er.) The solid 

 angles of a tetrahedron are formed 

 by three equilateral plane triangles, 

 and the solid is bounded by four 

 equal and equilateral plane tri- 

 angles, therefore it is a pyramid ; a 

 four-sided solid contained by four 

 equal- sided triangles ; a solid con- 

 tained by four triangular surfaces. 



TnAi/icTRUM. } The name 



THALICTRO'IDES WEBSTERI. j given to 

 a fossil plant resembling the mea- 



dow-rue, and found in the London 

 clay. 



THA'LLITE. The name given by Leme- 

 therie to the Epidote of Hau'y, or 

 Pistazit of Werner. 



THA'LLUS. (from 0a\\os, a green 

 leaf, Gr.) In botany, a name given 

 to the frond, or leaf-like part, of 

 certain plants. Lichens, are stem- 

 less, leafless plants, consisting of a 

 tough wrinkled substance, called a 

 thallus, 



THA'LOGEN. The thalogens constitute 

 a class of plants comprising four 

 orders; algas, fungi, lichens, and 

 characese. 



THE'CA. (from Ofay, Gr. theca, Lat.) 

 A case or sheath. The sporules of 

 plants are contained within thecae. 



THECODONTOSAU'RTJS. A genus of fos- 

 sil saurians, found in the magnesian 

 limestone : the vertebrae are deeply 

 concave at each end. 



THELO'DUS. (from #17X1), mamilla, 

 and oovs, dens, Gr. mammillated 

 tooth.) A genus of ichthyolites 

 discovered in the Upper Ludlow 

 rock, and thus named by Agassiz. 

 The teeth of the Thelodus resemble 

 in some respects those of the Lepi- 

 dotus. One species only is descri- 

 bed, namely, Thelodus parvidens. 



THE'RMAL. (thermal, Fr. Oep/ib<t, 

 warm, Gr.) A term applied prin- 

 cipally to warm springs and waters. 

 The temperatures of different ther- 

 mal springs vary greatly from each 

 other, but the same spring is found 

 to be of a uniform temperature at 

 all seasons of the year. Thermal 

 waters are found to be, on the aver- 

 age, neither more nor less pure 

 than springs of common tempera- 

 ture. It appears, from Dr. Dau- 

 beny's researches, that nitrogen 

 gas is very common in hot springs, 

 and, perhaps, very rare in cold 

 waters. Thermal waters prove the 

 extensive effects of subterranean 

 heat, deriving their temperature 

 from a deep-seated internal source 

 of heat, and not from any local 



