530 



Crcas'urj) of Natural f^t'story ; 



during the first autumn is a nearly uniform 

 green, which is gradually changing to a 

 party-coloured livery of scarlet, blue, and 

 green, till it assumes the rich and well- 

 defined colours of the adult. 

 PLATYPUS. [See ORNITHORHYNCUS.] 

 PLATYRRHINI. The name given to a 



division of the Qttadrumana, comprehending 

 " Tonkey-like animals 

 belonging to the New World. They are 



all the large species of Monkey-like ani 



characterized by having thirty-six grinders 

 (being four more than the others) ; the tail, 

 in general, long ; and in some species pre- 

 hensile ; no cheek-pouches ; posteriors hairy 

 and without callosities ; nostrils opening on 

 the sides of the nose, and not underneath. 

 [See MONKEY.] 



PLECTOGNATHI. Thenameofan 

 order of fishes, in some measure connecting 

 the osseous with the cartilaginous kinds ; 

 comprehending those which have the jaws 

 formed by the maxillary bones being anchy- 

 losed to the sides of the intermaxillaries. 



PLESIOSAURUS. The name of a genus 

 of extinct marine Saurians, of gigantic di- 

 mensions, which may be thus described : 

 the head short, somewhat oblong, and obtuse ; 

 the neck extremely long, consisting of about 

 thirty-three vertebrae ; body elongated ; tail 

 short ; nostrils small ; teeth numerous, lodged 

 in small alveoli ; ribs composed of two parts, 

 the one vertebral and the other ventral, the 

 vertebral column consisting of about ninety 

 joints That in the earlier periods of animal 

 existence reptiles were created of much 

 greater dimensions, and were far more nu- 

 merous in proportion, than at present, seems 

 evident from the discovery and examination 

 of the organic remains which from time to 

 time have come under the observation of 

 men of science ; and there is scarcely any 

 one more entitled to our notice, on account 

 of its extraordinary form than the Plesio- 

 saurus. Its neck is five times the length of 

 its head ; the trunk of the body four times 

 the length of the head ; and the tail three 

 times ; while the head itself is only a thir- 

 tieth part of the whole body. From the 

 whole physiology of the animal, Mr. Cony- 

 beare says, that it was aquatic is evident 

 from the form of its paddles ; that it was 

 marine, is almost equally so, from the 

 remains with which it is universally as- 

 sociated ; that it may have occasionally 

 visited the shore, the resemblance of its 

 extremities to those of the Turtle may 

 lead us to conjecture ; its motion, however, 

 must have been very awkward on land : its 

 long neck must have impeded its progress 

 through the water, presenting a striking 

 contrast to the organization which so ad- 

 mirably fits the Ichthyosaurus to cut through 

 the waves. May it not, therefore, be con- 

 cluded, (since, in addition to these circum- 

 stances, its respiration must have required 

 frequent access of air,) that it swam upon or 

 near the surface ; arching back its long neclc 

 like the swan, and occasionally darting it 

 down at the fish which happened to float 

 within its reach. It may perhaps have lurked 

 in isJioal water along the coast, concealed 



among the sea-weed, and, raising its nostrils 

 to a level with the surface from a consider- 

 able depth, may have found a secure retreat 

 from the assaults of dangerous enemies ; 

 while the length and flexibility of its neck 

 may have compensated for the want of 

 strength in its jaws, and its incapacity for 

 swift motion through the water by the sud- 

 denness and agility of the attack which they 

 enabled it to make on every animal fitted 

 for its prey. The remains of the Plesio- 

 sauri occur in the formations from the mus- 

 chel-chalk to the chalk inclusive ; but are 

 most common in the lias and Kimmeridge 

 clay beds. They were discovered in Eng- 

 land, and have since been found in France 

 and Germany. 



" It is of the Plesiosaurus," says Dr. Buck- 

 land, " that Cuvier asserts the structure to 

 have been the most heteroclite, and its cha- 

 racters altogether the most monstrous that 

 have been yet found amid the ruins of a 

 former world. To the head of a lizard it 

 united the teeth of a crocodile ; a neck of 

 enormous length, resembling the body of a 

 serpent ; a trunk and tail having the pro- 

 portions of an ordinary quadruped, the ribs 

 of a chameleon, and the paddles of a whale. 

 Such are the strange combinations of form 

 and structure in the PJesiosaurus a genus, 

 the remains of which, after interment for 

 thousands of years amidst the wreck of mil- 

 lions of extinct inhabitants of the ancient 

 earth, are at length recalled to light by the 

 researches of the geologist, and submitted to 

 our examination in nearly as perfect a state 

 as the bones of species that are now existing 

 upon the earth." The finest collection of 

 remains of the Plesiosaurus is in the British 

 Museum. [See ICHTHYOSAUKUS.] 



PLEUROBRANCHUS. A genus of ma- 

 rine Mollusca, having a very light thin in- 

 ternal shell ; nearly flat, and obliquely oval ; 

 slightly convex towards the spiral apex. It 

 is found in the Indian seas and the Mediter- 

 ranean. 



PLEURONECTID^E. The name of a 



family of Malacopterygious fishes, commonly 

 known by the appellation of Flat-Jifh. They 

 are distinguished not only from all other 

 Fishes, but even from all other vertebrated 

 animals, by several peculiarities of structure. 

 Their body is extremely compressed, or flat- 

 tened at the sides. Both eyes are on one 

 side, and this side always remains upper- 

 most when the animal is swimming. The 

 upper side is in general deeply coloured, 

 while the other side is whitish. The two 

 sides of the mouth are not equal, and the 

 pectoral fins are rarely so. The body is de- 

 pressed, and elevated m the direction of the 

 spinous processes ; the dorsal extends along 

 the whole back ; the anal occupies the lower 

 edge of the body, and the ventrals are some- 

 times united with it. They have six gill- 

 rays ; the abdominal cavity is small, but ex- 

 tends in a cavity imbedded in the flesh on 

 the two sides of the tail, for the purpose of 

 containing some of the viscera : they have 

 no air-bladder, and they seldom rise farfrom 

 the bottom ; but when disturbed, they will 

 raise themselves into a vertical position, so 



