SCR 



fishes, characterized by their very hard 

 and granulated skins. The roughness of 

 the skin in some of the species has sug- 

 gested the common term of file-fishes. 



SCLE'ROGEN (o-KXrjpof, hard, fevvdta, 

 to produce). The matter of lignification 

 which is deposited on the inner surface 

 of the cells of plants, contributing to 

 their thickness. 



SCO'LIADiE. A family of fossorial 

 hjanenopterous insects, named from the 

 genus scolia. 



SCOLOPA'CIDiE {scolopax, the wood- 

 cock). The Snipe tribe ; a family of the 

 Grallatores, or Wading birds, charac- 

 terized by their long, slender, and feeble 

 bill. 



SCOLYMI'NiE. A sub-family of the 

 Turbinellidce, or Turnip-shells, named 

 from the typical genus scolymus, and 

 characterized by a ponderous and rough 

 shell, with foliated spines or tubercles. 



SCOMBE'RID^ {scomber, the mack- 

 erel). The Mackerel tribe ; a family of 

 the Acanthopteryginus or spiny-finned 

 fishes, including the mackerel, tunny, 

 sword-fish, dory, dolphin, &c. 



SCO'PIPEDS {scopce, a brush, pes, a 

 foot). A tribe of melliferous insects, in- 

 cluding those which have the tarsi of 

 the posterior feet furnished with a brush 

 of hairs. 



SCORIA {oKuypia, from (TKcbp, excre- 

 ment). The scum or dross of metals ; 

 the refuse or useless part of any sub- 

 stance ; volcanic cinders ; &c. 



SCO'RPIO. The Scorpion ; the eighth 

 of the zodiacal constellations, consisting 

 of forty-four stars, the principal of which 

 is Antares., It denotes the second month 

 of spring, extending from the 20th of 

 April to the 20th of May. The heat of 

 this month stimulates venomous rep- 

 tiles, and excites disease and pesti- 

 lence. 



SCREW. One of the mechanical 

 powers. It may be considered as an in- 

 clined plane wrapped round a cylinder, 

 or as a cylinder having on its surface a 

 projecting thread inclined in all parts at 

 the same given angle to the horizon. 

 The cylinder fits into a block pierced 

 with an equal cylindrical aperture, on 

 the inner surface of which is cut a 

 groove, the exact counterpart of the 

 thread on the screw; hence we can 

 cause the screw to enter the block by 

 merely making it revolve about its 

 axis. 



Endless Screw. The force of the screw 

 is sometimes employed to turn a wheel, 

 298 



SEA 



by acting on its teeth, the thread of the 

 screw passing between the teeth or cogs 

 of the wheel. In this case it is called a 

 perpetual or endless screw. 



SCROPHULARlA'CEiE. The Fig- 

 wort tribe of Dicotyledonous plants. 

 Herbaceous plants with leaves opposite ; 

 flowers irregular, unsymmetrical ; sta- 

 mens 2 or 4, didynamous ; fruit capsular; 

 seeds albuminous. 



SCURF OF PLANTS. A term ap- 

 plied in Botany to the thin, flat, mem- 

 branous disks, with a ragged margin, 

 formed of cellular tissue, springing from 

 the epidermis of plants. They are dis- 

 tinguished into scurf, properly so called, 

 and ramenta. 



SCUTE'LLUM (dim. of scutum, a 

 shield). Apothecium. The botanical de- 

 signation of the little coloured cup or 

 disk, found in the substance of lichens ; 

 it is surrounded by a rim, and con- 

 tains the asci, or tubes filled with spo- 

 rules. 



SCUTIBRANCHIA'TA {scutum, a 

 shield, branchice, gills). An order of 

 gasteropods which have pectinated gills 

 disposed in a special cavity, with shells 

 which are very wide, scarcely ever turbi- 

 nated, and cover the body and gills, 

 like a shield. 



SCU'TIPEDS {scutum, a shield, pes, a 

 foot). The name given by Scopoli to 

 those birds which have the anterior part 

 of the leg covered with segments of un- 

 equal horny rings terminating on each 

 side in a groove. 



SCUTUM SOBIESKI. Sobieski's 

 shield ; a modern northern constella- 

 tion, consisting of eight stars. 



SCYLLA'RIANS. A tribe of macru- 

 rous decapods, established by Milne 

 Edwards on the genus scyllarus of Fa- 

 bricius, and forming one of the most re- 

 markable groups, distinguished at the 

 first glance by the singular conformation 

 of the external antennae. It comprises 

 the genera Scyllarus, Thenus, and Iba- 

 cus. 



SEA. A portion of the ocean which 

 penetrates into a continent by a narrow 

 passage, and then spreads into a large 

 expanse, as the Mediterranean sea. The 

 term is, however, frequently employed 

 in a larger sense to denote the whole 

 volume of water which occupies the 

 lower portion of the surface of our globe, 

 or three-fourths of its entire superficies ; 

 in this sense it is synonymous with 

 ocean. 

 SEA WAX. Maltha; a white, solid, 



