822 



NORTH AMERICAN INDEX FOSSILS. 



Arenaceous — of the texture or charac- 

 ter of sand. 



Areole {areola) — in echinoids, the 

 smooth sunken area surrounding the 

 base of the tubercle (see IT., 575, 

 and Fig. 19 18, h, c). 



Argillaceous — of clay or slate. 



Arikarie — lower Miocenic of Nebraska. 



Aristotle's lantern — the complicated 

 dental apparatus of echinoids. 



Arkansan — lower Coal Measures of 

 central United States. 



Articulated — joined by interlocking 

 processes or by teeth and sockets. 



Ashley River marls — lower Miocenic of 

 South Carolina. 



Asperate — rough. 



Astoria shales — Oligocenic of western 

 Oregon. 



Astrorhisce — branching grooves, often 

 present on the surface of hydrocoral- 

 lines (see I., 35). 



Atoka shales — subdivision of the Ar- 

 kansan of Oklahoma. 



Attenuate — to taper, to become thin or 

 slender. 



Aubrey group — Coal Measures of Grand 

 Canyon. 



Auricle — ear, or anterior projection of 

 the hinge of many pelecypods. 



Auriculate — having ears. 



Austin chalk — lower Cretacic (Colora- 

 doan) of Texas. 



Avicularia — in many broyozoa, prehen- 

 sile projections, shaped like a bird's 

 head ; incapable of preservation in the 

 fossil state, but their former presence 

 may usually be noted in the slight, 

 pore-like hollows in which they were 

 lodged. 



Aviculoid — resembling Avicula ; winged. 



Axial — pertaining to the axis. 



Axial canal — central canal of a cri- 



noid stem. 

 Axial furrows — furrows or depres- 

 sions bordering the axis in trilo- 

 bites. 



Axillaries — for use in crinoids, see II., 

 490. 



Axis — the central longitudinal division 

 of the body of a trilobite. 



Azygous — unpaired. In crinoids, that 

 side of the calyx which has plates dif- 

 fering from those of the regular 

 sides. In cephalopods, referring to 

 the unpaired lobes — the siphonal and 

 antisiphonal. 



Bactriticone — a straight Ammonoid 

 shell (see II., 19). 



Bajocian — division of middle Jurassic. 



Bangor limestone — upper Mississippic, 

 southern Appalachians. 



Barker series — middle Cambric, Mon- 

 tana. 



Basals — the lowest cycle of plates in 

 crinoids with monocyclic base; in 

 crinoids with dicyclic base, the row 

 of plates next above the infrabasals 

 (see Figs. 1876, 1907B). For use in 

 echinoids, see genital plates. 



Basipodite — see II., 388. 



Batesville sandstone — see Cypress sand- 

 stone. 



Bays sandstone — upper Ordovicic, 

 southern Appalachians. 



Beak — in bivalve shells, the projecting 

 part of each valve near the hinge ; it 

 is where the growth of the valves be- 

 gan (see I., 172). 



Bear River — non-marine Coloradoan. 



Beaver limestone — lower Cambric, 

 southern Appalachians. 



Becraft limestone — division of the Hel- 

 derbergian. 



Bedford oolite — see Salem limestone. 



Bedford shale — division of the Waverly. 



Beekmantownian — a general term for 

 the lower Ordovicic. 



Beekmantown limestone — lower Ordo- 

 vicic, eastern North America. 



Belly River — non-marine Montanan of 

 Canada. 



Bend formation — lower Carbonic of 

 Texas. 



Benthonic — referring to the benthos. 



Benthos — an organism which inhabits 

 the bottom of the sea. 



