M L 



L 300 ] M 



of the world. Some of these, as 

 the orthoceratite, spirifer, and pro- 

 ducta, became extinct at an early 

 period in the history of stratified 

 rocks, whilst others as the tere- 

 bratula and nautilus, have con- 

 tinued through all formations to 

 the present time. Cumer. Grant. 

 Kirty. Roget. 



MOLLTJSCOID'EA. The third class of 

 the sub-kingdon Mollusca : this 

 class comprises three orders, name- 

 ly, Brachiopoda, Polyzoa, and 

 Ascidioida, or Tunicata. 



MOLLTJ'SCOUS. Animals belonging to 

 the division mollusca, or soft, in- 

 vertebral, inarticulate animals ; 

 often protected by a shell. 



MOLLTJ'SKITE. The soft bodies of the 

 testaceous mollusca often occur in 

 a fossil state, changed into a brown 

 carbonaceous substance, to which 

 Dr. Mantell assigned the above 

 name. 



MOLY'BDATE OF LEAD. The plomb 

 molybdate of Haiiy; pyramidaler 

 blaibaryt of Mohs. Yellow lead 

 ore. It is of a yellow colour, 

 varying from lemon yellow to yel- 

 lowish brown. Occurs crystallized 

 and massive. Its specific gravity 

 from 6-5 to 6-9. Fracture uneven, 

 or imperfectly conchoidal. Slightly 

 translucent, especially at the edges. 

 Before the blow-pipe it decrepitates, 

 and fuses into a dark coloured mass. 

 It consists of oxide of lead 58, 

 molybdic acid 38, oxide of iron, 2. 

 It is found at Bleyberg, in Car- 

 inthia, and in Mexico, in compact 

 limestone. 



MOLYBDE'NA. A mineral of a lead- 

 grey colour, occurring in thin flexi- 

 ble leaves. 



MOLYBDE'NTTM. (from fiokvpSaiva, Gr. ) 

 A metal discovered by Hielm in 

 1782; externally of a whitish yel- 

 low colour ; fracture whitish grey : 

 sp. gr. about 8-6. It is nearly 

 infusible. It is obtained from the 

 mineral molybdena in small grains, 



agglutinated together in brittle 

 masses. 



MO'NAD. (from povas, Gr. an atom, 

 monade, Fr.) The recent observa- 

 tions of Professor Ehrenberg have 

 brought to light the existence of 

 monads, which are not larger than 

 the 24,000th of an inch, and which 

 are so thickly crowded in the fluid 

 as to leave intervals not greater 

 than their own diameter. Hence 

 he has made the computation that 

 each cubic line, which is nearly 

 the bulk of a single drop, contains 

 500,000,000 of these monads; a 

 number which equals that of all 

 the human beings on the surface 

 of the globe in one drop of fluid. 

 Monads, which are the smallest of 

 all visible animalcules, have been 

 spoken of as constituting "the ulti- 

 mate term of animality." 



MoNA'tfPKiA. (from /AoVos, one, and, 

 avfjp, a man, Gr.) The first class 

 of plants in Linnasus's artificial 

 system. The plants of this class 

 have only one stamen; it is a small 

 class, and contains only two orders. 



MONI'LIFORM. (from monile, a neck- 

 lace, and forma, form, Lat.) Ee- 

 sembling a necklace 



MO'NITOB. (monitor, Lat.) A genus 

 of lizards or saurians, species of 

 which are found both fossil and 

 recent; the recent inhabit the 

 tropics. Cuvier places this genus 

 in the family Lacertinida. The 

 monitors frequent marshes, and the 

 banks of rivers, in hot climates; 

 they have received their name from 

 a common but silly notion that 

 they give warning of the approach 

 of crocodiles and caymans by a 

 whistling noise. One species, the 

 Lacerta nilotica, devours the eggs 

 of crocodiles. Fossil remains of 

 the monitor have been discovered 

 in the strata of Tilgate Forest, in 

 Sussex. 



MONOCOTYLE'DON. (from /toVos, one, 

 and Korv\r]Swv, a seed lobe, Gr.) 



