PET 



PET 



parted, very large, coloured; corolla 

 wheel shaped; capsule two-celled, at 

 the bottom of the calyx ; seeds solitary. 

 There is but one species, viz. P. volu- 

 bilis, a native of South America and the 

 West Indies. 



PETRIFACTION. See OUYCTOLOG*-. 



PETROCARYA, in botany, a genus 

 of the Heptandria Monogynia class and 

 order. Natural order of Pomaceae. Ro- 

 sace ae, Jussieu. Essential character : ca- 

 lyx turbinate, five-cleft, with two bractes 

 at the base ; corolla h've-petalled, less 

 than the calyx ; filaments fourteen, se- 

 ven of which are barren ; drupe in- 

 closing a two-celled nut, with a stony 

 shell. There are two species, viz. P. 

 montana, and P. campestris, both found 

 in the woods of Guiana, where they 

 grow to the height of forty and eighty 

 feet. 



PETROLEUM, in chemistry. The 

 substances which mineralogists have dis- 

 tinguished by the names of asphaltum, 

 maltha, petroleum, and naptha, are 

 thought by Mr. Murray, and others, to 

 be mere varieties of one species, and 

 form a series which passes even into coal. 

 Asphaltum forms the connection with 

 pitch-coal. It is found in veins, and in 

 small masses, and also sometimes on the 

 surface of lakes. Maltha is softer, has a 

 degree of tenacity, and a strong bitumi- 

 nous smell. Petroleum is semi-liquid, 

 semi-transparent, of a reddish-brown co- 

 lour, andfetid odour. Naptha is of a lighter 

 colour, more or less transparent, perfectly 

 thin and liquid, light, odoriferous, vola- 

 tile, and inflammable. Naptha by inspis- 

 sation becoming petroleum, and this pass- 

 ing into asphaltum. See ASPHALTUM, Bi- 



TUMEX, &.C. 



In several parts of France petroleum is 

 found floating on the water, and is known 

 in commerce by the name of oil of Gabian. 

 Wells are sometimes dug 109 feet deep, 

 \vhere the petroleum is found mixed with 

 the soil, in such proportion that ten 

 pounds may be extracted from a hundred 

 weight. 



PETROMYZOX, the lamprey, in natu- 

 ral history, a genus of fishes of the order 

 Cartilaginei. Generic character : body 

 shaped like an eel ; mouth beneath, with 

 numerous teeth, in circular rows ; seven 

 spiracles on each side the neck ; no pec- 

 toral or ventral fins. Shaw notices nine 

 species, and Gmelin only four. P. mari- 

 nus, or the great lamprey, is usually of a 

 brown olive colour, tinged with yellowish 

 white. It is often three feet long ; is an 

 inhabitant of the seas, as its name indeed 



implies ; but in the beginning of spring 

 ascends rivers, in which it resides for a 

 few months, then returning to the ocean. 

 It is viviparous, and supposed to subsist 

 almost entirely on worms and fishes. Its; 

 heart is enclosed not in a soft but in a car- 

 tilaginous pericardium, constituting thus 

 a singular deviation from the general 

 structure of animals. Its spine also pos- 

 sesses the peculiarity of being rather a 

 soft cartilage than bone. These fishes 

 fasten themselves with the jagged edges 

 of the mouth to large stones, with the 

 most extraordinary firmness, and may be 

 lifted by the tail to a considerable height, 

 without being made to quit a stone of the 

 weight of even ten or twelve pounds. 

 Their principle of vitality is extremely vi- 

 gorous and persevering, various parts of 

 the body long continuing to move for 

 some hours after it is divided; and the 

 head will adhere to a rock for hours after 

 the greater part of the body is cut away. 

 In some large rivers of Europe, these 

 fishes are taken in vast numbers, and pro- 

 served with spices and salt as an article 

 for merchandise. In England, the Severn 

 is the most celebrated river for them, and 

 they are much valued on their first arri- 

 val from the sea. They are considered a 

 high luxury for the table, and the life of 

 one of the Kings of England will be recol- 

 lected to have been terminated by his ex- 

 cessive partiality to potted lampreys. 



P. fluviati'is, or the lesser lamprey of 

 Europe, is about twelve inches long, in- 

 habits also the sea, but is found more 

 frequently in the rivers than the former. 

 It abounds in the Thames and Severn, and 

 is preferred by many to the larger species, 

 as being not so strong in taste. In some 

 years half a million of these fishes have 

 been sold from the neighbourhood of 

 Mortlake, for the Dutch cod and turbot 

 fishery, at the rate of two pounds per 

 thousand. In many parts of Germany 

 they are fried and packed up in barrels 

 with spices and bay leaves, and are con- 

 veyed to very distant regions, where they 

 are in high estimation, and sell for consi- 

 derable prices. These fishes will live ma- 

 ny days out of the water. In Russia 

 they are taken from beneath the ice, pack- 

 ed in snow, and exported to great dis- 

 tances, and will generally recover them- 

 selves on being afterwards thrown into 

 the water. The planer lamprey is ten 

 inches long, will live immersed in spirits 

 of wine for fourteen minutes, moving dur- 

 ing that time with incessant violence. 

 The leech lamprey is a native of the rU 

 ver Seine, and will fix on the bellies of va- 



