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words ; it implies a sense of spuri- 

 ousness, as, for example, a pseudo- 

 tuber is a false tuber; pseudo- 

 galena is false galena; a pseudo- 

 volcano is a coal mine in a state of 

 combustion. 



PSEUDOMO'RPH. (from tyevSos, false, 

 and floppy, form, Gr.) A Pseudo- 

 morph is one mineral occurring in 

 the crystalline form of another. 



PSEUDOMORPHISM. That process by 

 which the constituents of minerals 

 are changed, and the place of the 

 removed constituent is supplied by 

 the presence of another of the same 

 form. 



PTERA'SPIS. A generic name proposed 

 by Dr. R,. Kner, and accepted by 

 Mr. Salter, for certain species of 

 Cephalaspis, namely C. Lewisii, 

 and C. Lloydii. 



PTERIC'HTHYS. (from Tnepvg, a wing, 

 and i'xQvs, a fish, Gr.) The winged 

 fish, an ichthyolite of the lower 

 old red sandstone. Hugh Miller 

 thus graphically describes the pte- 

 richthys, "on a ground of light 

 coloured limestone, lay the effigy 

 of a creature fashioned apparently 

 out of jet, with a body covered 

 with plates, two powerful-looking 

 arms articulated at the shoulders, 

 a head as entirely lost in the trunk 

 as that of the ray or the sun-fish, 

 and a long angular tail. This ich- 

 thyolite in my large specimens 

 does not much exceed seven inches 

 in length." Agassiz has distin- 

 guished nine species. 



PTERO'CERES. A genus of- winged 

 zoophagous univalves; they are 

 turrited, oval, ventricose, and tuber- 

 culated, the spire is short, the 

 aperture oval, terminating in a 

 lengthened canal at both extremi- 

 ties ; the outer lip is thickened, 

 expanded into horn-shaped, hollow, 

 thickened spines with an anterior 

 sinus apart from the caudal canal. 

 Several fossil species are recorded 

 from the Jurassic and Cretaceous 

 rocks of Franco and Germany. 



PTESODA'CTTLE. ) (from Tnepov, a 



PTERODA'CTYLTJS. j wing, and 

 TvX.o?, a finger, Gr.) An extinct 

 genus of winged reptiles, belong- 

 ing to the family Iguanida. It is 

 found fossil in the Jura limestone 

 formation, in the lias at Lyme 

 Regis, and in the oolitic slate of 

 Stonesfield. "The structure of 

 these animals," says Buekland, "is 

 so exceedingly anomalous, that the 

 first discovered pterodactyle was 

 considered by one naturalist to be 

 a bird; by another, a species of 

 bat ; and by a third, a flying rep- 

 tile. The form of its head and 

 length of neck, resembled that of 

 birds, its wings approached to the 

 proportion and form of those of 

 bats, and its body and tail approxi- 

 mated to those of ordinary mam- 

 malia. The pterodactylus forms 

 an extinct genus of the order Sau- 

 rians, in the class of reptiles; 

 adapted by a peculiarity of struc- 

 ture to fly in the air." The ptero- 

 dactyles are considered by Cuvier 

 to rank among the most extraordi- 

 nary of all the extinct animals that 

 have come under his consideration. 

 Species have been discovered, of 

 sizes varying from that of a snipe 

 to that of a cormorant. They had 

 a short tail, an extremely long 

 neck, and a very large head ; their 

 eyes were of enormous size, appar- 

 ently enabling them to fly by night; 

 the beaks were long, like those of a 

 crocodile, and furnished with sixty 

 sharp-pointed teeth. Their most 

 remarkable character consisted in 

 the excessive elongation of the se- 

 cond toe of the fore-foot, which 

 was more than double the length 

 of the trunk, and, in all proba- 

 bility, served the purpose of sup- 

 porting some membrane which en- 

 abled the animal to fly. The fingers 

 terminated in long hooks, like the 

 curved claws of the bat. The form 

 and size of the foot, leg, and thigh, 

 show that this extraordinary ani- 





