GAP 



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G A V 



dean, then for the first time intro- 

 duced. Ib. 



GAP. In conchology, an opening, in 

 multivalves and bivalves, when the 

 valves are shut, as in the pholades, 

 myse, &c. 



GARNET, (grenat, sorte depierre pre- 

 cieuse, $un rouge fonce, comme legros 

 vin, Fr. granato, It. pietrapreziosa.J 

 Prof. Jameson, in his system of 

 Oryctognosy, constitutes a family 

 of earthy minerals which he deno- 

 minates the garnet family; this 

 consists of Leucite, Vesuvian, 

 Grossular, Melanite, Allochroite, 

 Garnet, Grenatite, Pyrope, and 

 Cinnamon Stone. The precious 

 garnet is found in rhombic dode- 

 cahedrons, in mica- slate, amongst 

 the oldest, or primary, rocks, in 

 many parts of the world. It is of 

 a beautiful red colour, sometimes 

 with shades of yellow or blue. 

 Those from the kingdom of Pegu 

 are most esteemed, and it is sup- 

 posed that this was the carbuncle 

 of the ancients. It is harder than 

 quartz, and consists of nearly equal 

 parts of silex, alumine, and oxide 

 of iron, with traces of manganese. 

 Common garnets are more opaque, 

 of a duller colour, and less hard 

 than the precious garnet, though 

 harder than quartz. They are 

 abundant in similar localities in all 

 countries, sometimes constituting 

 nearly the whole mass of a rock. 



GAS. The name given to all perma- 

 nently elastic, or aeriform, fluids, 

 except the atmosphere. The term 

 was first used by Yan Helmont, 

 who appears to have intended to 

 denote by it every thing which is 

 driven off from bodies in the state 

 of vapour by heat. 



GASTE'EOPOD. Belonging to the order 

 Gasteropoda. 



GASTEEO'PODA. (from ^aa^p, the 

 belly, and TTOVS, the foot, Gr.) 

 The third order of Mollusca ; they 

 have the head free, they crawl 

 upon the belly, or upon a fleshy 



disk, situated under the belly 7 

 which serves them as feet. They 

 are univalvular or multivalvular, 

 but in no case bivalvular. The 

 back is furnished with a mantle 

 which is more or less extended, 

 takes various forms, and in the 

 greater number of genera, produces 

 a shell. The tentacula are very 

 small, situated above the mouth, 

 and do not surround it, varying in 

 number from two to six; sometimes 

 they are wanting altogether. The 

 eyes are very small, and sometimes 

 wanting. Several are entirely 

 naked ; others have merely a con- 

 cealed shell, but most of them are 

 furnished with one that is large 

 enough to receive and shelter them. 

 Most of the aquatic gasteropoda, 

 ' with a spiral shell, have an oper- 

 culum, a part sometimes horny, 

 sometimes calcareous, attached to 

 the posterior part of the foot, 

 which closes the shell when its 

 occupant is withdrawn into it and 

 folded up. The limax or slug is 

 an example of the class. Cuvier 

 divides this class of Mollusca into 

 nine orders. 



GA'STBIC. (from ^aa^p, Gr. gastrique, 

 Pr. gastrico, It.) Belonging to the 

 stomach or belly. 



GAULT. See Gait. 



GA'VIAL. A subdivision of the genus 

 crocodile, characterized by the nar- 

 row, elongated, almost cylindrical 

 jaws, which form an extremely 

 lengthened muzzle. The muzzle 

 is narrow, cylindrical, extremely 

 elongated, and a little swelled out 

 at the ends. The length of the 

 cranium is scarcely one-fifth of the 

 entire length of the head. The 

 teeth are nearly equal, twenty-five 

 to twenty- seven on each side below. 

 The first two and fourth two of the 

 lower jaw pass into notches of the 

 upper, and not into hollows. The 

 cranium has large foramina behind 

 the eyes, and the hind feet are 



