850 



NORTH AMERICAN INDEX FOSSILS. 



Schizodont dentition — in pelecypods, 

 with coarse, variable, amorphous 

 teeth, as Unio. 



Schoharie beds — basal middle Devonic 

 of New York, etc. 



Sclerenchyma — calcareous tissue depos- 

 ited by the coral polyp. 



Sclerite — a hard separate skeletal ele- 

 ment, as in corals and insects (see 

 II., 419). 



Scrobicula — see areola. 



Scrobicular — pertaining to scrobiculae 

 (areolae). 



Scrobicular circle — in echinoids, the 

 ring of granules marking the outer 

 limit of the areole (see Fig. 1918, 

 b, c). 



Scuta — in Balanus, the more horizontal 

 of the two pairs of movable plates 

 which form the operculum. 



Scutellum — see IL, 420. 



Scutum — see II., 420. 



Scythic — division of the lower Triassic. 



Sedentary — stationary, not moving from 

 place to place. 



Sediment — its influence on life, I., 2. 



Segment — one of the parts into which a 

 body naturally separates. In trilo- 

 bites, the varying number of divisions 

 of the thorax articulating with one 

 another. 



Sellersburg beds — middle Devonic of 

 Indiana. 



Semi — a prefix, meaning half. 



Semilunar — crescentic, or resembling a 

 half moon. 



Semiovate — half egg-shaped. 



Senecan series — upper Devonic of east- 

 ern North America. 



Senile — old. 



Septal — pertaining to a septum. 



Septal radii — radiating ridges taking 

 the place of septa in certain corals. 



Septate — with partitions or septa. 



Septum (plural septa) — a wall or par- 

 tition. In corals, one of the radiat- 

 ing calcareous plates (see Fig. 162; 

 for cardinal, counter and lateral or 

 alar septa, see Fig. 75 ; see also mes- 

 entery). In some brachiopods, the 



median ridge on the inside of the 

 valves extending forward from the 

 beak (see Figs. 382, lower right, and 

 407, S). In cephalopods, the trans- 

 verse partitions between the cham- 

 bers (see Fig. 1230). 



Sequanian (Corallian) — division of up- 

 per Jurassic. 



Serrate — notched like a saw, with sharp 

 notches. 



Sessile — attached by a broad base, not 

 by a stalk. 



Seta (plural setce) — a bristle ; a stiff, 

 stout hair. 



Setigerous — bristle-bearing. 



Sevier shales — upper Ordovicic of the 

 eastern Appalachians. 



Sewickley formation — upper Carbonic 

 of Ohio, Pennsylvania, etc. 



Shakopee dolomite — lower Ordovicic of 

 upper Mississippi Valley. 



Shandon quartzite — upper ( ?) Cambric 

 of the Rio Grande. 



Shark River beds — lower Eocenic of 

 New Jersey. 



Sharon group — upper Pottsville of 

 Ohio. 



Shasta group — the Comanchic of the 

 Pacific coast. 



Shawangunk conglomerate — middle Si- 

 luric of eastern United States. 



Shawnee group — upper Carbonic of 

 Kansas. 



Shelby dolomite — Guelph of New York. 



Shenandoah group — lower Cambric to 

 lower Ordovicic of southern Appa- 

 lachians. 



Shenango shale — upper Mississippic of 

 western Pennsylvania, etc. 



Sherbrook formation — upper Cambric of 

 Canadian Rockies. 



Shinarump formation — lower Triassic 

 of Colorado. 



Shirley formation — upper Jurassic of 

 Wyoming. 



Shoulder — in gastropods, see I., p. 583. 



Sicula — in graptolites, the earliest hy- 

 drotheca of a colony (see Figs. 40, 

 49). 



I 



