854 



NORTH AMERICAN INDEX FOSSILS. 



Tergite — see II., 420. 



Test — the protective covering of some 

 invertebrate animals. Shell is ap- 

 plied to such covering of brachiopods 

 and mollusks, where it is secreted by 

 a mantle ; test to that of echinoids, 

 crustaceans, etc., where the secre- 

 tion is internal or by the whole sur- 

 face of the body. 



Tetrameral — in corals, the arrangement 

 of all the septa of an individual into 

 four groups. 



Theca — the bounding wall of a coral 

 growing as an independent structure 

 from the bottom of the cup, as do 

 the septa, and connecting the outer 

 edges of the septa. 



Thecal — pertaining to a wall. 



Thoracic — pertaining to the thorax. 



Thorax — central part of the body of 

 trilobites and other arthropods (see 

 Fig. 1542). 



Tibia — in insects, that segment of the 

 leg next the foot (see IL, 420). 



Tichenor limestone — middle Devonic of 

 New York. 



Tinton formation — middle Cretacic of 

 Atlantic coast. 



Tirolic divisions — part of upper marine 

 Triassic. 



Tithonian — upper Jurassic (including 

 both Portlandian and Purbeckian). 



Tomstown limestone — lower Cambric of 

 Pennsylvania. 



Torrejon group — lower Eocenic of New 

 Mexico. 



Trabecules — small rods or bars. In 

 corals, see I., 81. 



Trachice — in insects, air tubes penetrat- 

 ing the body. 



Transverse — at right angles to the 

 lengh. Applied also to shells which 

 are wider than long. 



Traverse group — middle Devonic of 

 Michigan. 



Travis Peak beds — lower Comanchic of 

 Texas. 



Trentonian — general name for upper 

 Ordovicic. 



Trenton limestone — upper Ordovicic of 

 New York, etc. 



Tri — a prefix, meaning three or three- 

 fold. 



Trigonal — three-angled. 



Trimerelloid — see I., 177, 3. 



Trinity (Trinitan) — general name for 

 the lower Comanchic. 



Trivium — in some echinoids, the three 

 anterior ambulacra approach one 

 another closely and are separated 

 from the two posterior ambulacra by 

 a wide space. The three anterior 

 form the " trivium," and the two pos- 

 terior the " bivium." 



Trochanter — in insects, that segment of 

 the leg next to the basal segment 

 (see II. , 420). 



Trochantin — see II. , 420. 



Trochiform — in form like Trochus; 

 cone-shaped (see I., 592, e). 



Trochoceracone — an asymmetrically 

 coiled Nautiloid shell (see II., 19, 

 and Figs. 1288 and 1290). 



Troy limestone — lower Cambric of 

 eastern New York. 



Tube-feet — in star-fish and sea-urchins, 

 the extensible, fleshy, foot-like pro- 

 trusions from the ambulacral areas, 

 by means of which the animal moves. 



Tubercle — a knob-like process. In 

 echinoids, see II., 574, and "Fig. 1918, 

 b,c). 



Tuberose — having knobs. 



Tubule — a small tube or pipe. 



Tullahoma formation — lower Mississip- 

 pic of Tennesee and Kentucky. 



Tully limestone — basal upper Devonic 

 of central New York. 



Tumid — swollen, inflated. 

 Turbinate — shaped like a top. In gas 

 tropods, those shells whose whorls 

 decrease rapidly from a broad base 

 to the pointed apex. 

 Turreted — furnished with one or more 

 turrets or towers. Applied to gastro- 

 pods with elongate shells composed 

 of many distinct whorls (see Fig. 

 1064). 



