MED 



[ 160 ] 



MEL 



marginal membrane, like the fold of a 

 mantle, extending loosely downwards from 

 the circumference. 



Medusae are met with of very various 

 sizes ; the larger abound in the seas around 

 our coasts, but immense numbers of the 

 more minute, and often microscopic, species 

 occur in every part of the ocean. In some 

 parts of the Greenland seas the number of 

 Medusae is so great, that in a cubic inch, 

 taken up at random, there are not fewer 

 than 64. In a cubic foot this will amount 

 to 110,592 ; and in a cubic mile, the num- 

 ber is such, that allowing one person 

 to count a million in a week, it would 

 have required 80,000 persons from the 

 creation of the world, to complete the 

 enumeration. Dr. Roget. Dr. Kidd. 



MEGALO'NYX. (from p-eyag, great, and 

 ovvZ,, a claw, Gr.) A huge fossil mam- 

 malian, of the order Edentata, and thus 

 named from the great size of its unguical, 

 or claw, bones. The remains of the 

 Megalonyx were discovered in the floor of 

 a cavern, in the limestone of Virginia, in 

 America. 



MEGAH'CHTHYS. (from /iycrc> great, and 

 t%0iic., a fish, Gr.) The name given to a 

 fossil sauroid fish, first discovered, by Dr. 

 Hibbert, in the limestone near the bottom 

 of the coal formation, near Edinburgh. 

 Specimens of Megalichthys have since 

 been obtained by Sir P. Grey Egerton, 

 Mr. Austin, and Mr. Murchison, in the 

 coal formation. 



MEGALOSAU'RUS. (from /jsyac;, great, and 

 ffavpog, a lizard, Gr. ) A genus of fossil 

 amphibious animals, of great size, belong- 

 ing to the saurian tribe. This genus was 

 established by Professor Buckland. Cu- 

 vier concludes, from a comparison of the 

 fossil bones with those of existing lizards, 

 the megalosaurus to have been an enor- 

 mous reptile measuring from forty to 

 fifty, or even seventy, feet in length, and 

 partaking of the structure of the croco- 

 dile and monitor. Remains of the mega- 

 losaurus have been found in the Oolite 

 and in the Wealden. This huge creature 

 appears to have been carnivorous, from 

 the form of its teeth, and its head termi- 

 nated in a straight and narrow snout. 



MEGAPHY'TON. (from ftsyac., great, and 

 0vroj/, a plant.) An extinct genus of 

 plants belonging to the order Conifera. 

 In the genus Megaphyton the stem is not 

 furrowed, and the leaf scars are very 

 large, resembling the shape of horse- 

 shoes, and arranged on each side of the 

 stem in two vertical rows. It is found in 

 the coal strata. 



MEGATHE'RIUM. (from [isyag, great, and 

 Oijplov, a beast, Gr.) An extinct animal, 

 of great size, belonging to the order Eden- 

 tata. Fossil remains of the Megatherium 



have been discovered in South America, 

 in the alluvial deposites of the Pampas. 

 The Megatherium was about eight feet 

 high, and its body twelve feet long ; it 

 united part of the structure of the arma- 

 dillo with that of the sloth. The relative 

 proportions of the extremities of the me- 

 gatherium differ greatly from those of 

 the sloth, and indeed from those of any 

 known animal. Its teeth prove that it 

 lived on vegetables, and its fore-feet, 

 robust, and armed with sharp claws, 

 show that roots were its chief objects of 

 search. Its hide appears to have been 

 covered with a bony coat of armour of 

 considerable thickness, the use of which 

 was probably defensive, not only against 

 the sharp claws of beasts of prey, but 

 also against the myriads of insects that 

 surrounded it. " Secure within the pano- 

 ply of his defensive armour," says Pro- 

 fessor Buckland, " where was the enemy 

 that would dare encounter this behemoth 

 of the Pampas ? a creature whose giant 

 carcase was encased in an impenetrable 

 cuirass, and who, by a single pat of his 

 paw, or lash of his tail, could in an instant 

 have annihilated the couguar or the cro- 

 codile." 



MEI'ONITE. (from ptiuv, less, Gr.) The 

 Meionit of Werner. A mineral, thus 

 named from its terminating pyramids 

 being lower than those of similar forms in 

 the other minerals. Meionite much re- 

 sembles Wernerite in the measures of its 

 angles, but the terminating faces of Wer- 

 nerite stand on the lateral faces of the 

 primitive form, whereas in the meionite 

 they correspond to the truncated lateral 

 edges of the primitive form. Meionite is 

 a prismato -pyramidal felspar. It occurs 

 in grains, or small crystals, whose more 

 common form is an eight-sided prism, 

 truncated on its lateral edges, and termi- 

 nated by four low-sided pyramids. It is 

 of a greyish-white colour ; translucent 

 and sometimes transparent. It scratches 

 glass, and before the blow-pipe readily 

 melts into a white spongy glass. It is 

 found at Mount Somma, near Vesuvius. 



MELA'NIA. (from fttXag, black, Gr.) A 

 genus of univalve fresh-water shells be- 

 longing to the order Pectinibranchiata, 

 class Mollusca. The melania is a tur- 

 reted univalve ; the aperture entire, ovate, 

 or oblong, and spread out at the base of 

 the columella, which is smooth. Recent 

 melanise are found in rivers and estuaries. 

 Fossil melaniae are found in the environs 

 of Paris. Lamarck describes twelve spe- 

 cies. 



ME'LANITE. (from jutXerf, black, Gr.) 

 The Melanit of Werner ; Grenat noir of 

 Haiiy ; Grenat melanit of Brongniart. A 

 velvet-black, opaque, dodecahedral variety 



