M Y A 



306 ] 



M T T 



ascidia. Shell transverse, oval, 

 thick, gaping at both ends; liga- 

 ment internal. Hinge with broad, 

 thick, strong, patulous tooth, sel- 

 dom more than one, perpendicular 

 to the valve, and giving attachment 

 to the ligaments. 



MY'LIOBATES. A genus of fossil Rays. 

 They are abundant in the London 

 clay and in the crag. 



MT'OLOGY. (from fiv$, '[wo?, a mus- 

 cle, and \oryov, discourse.) A 

 description of the muscles. 



MYO'POBA. A genus of bivalve con- 

 chifera, established by Lea, belong- 

 ing to the family Arcacea. 



MYBIAN'ITES. A genus of the !N"erei- 

 dina of Mac Leay; body linear, 

 very narrow, and formed of very 

 numerous segments, with indistinct 

 feet and short cirri. One species, 

 Myrianites Mac Leaii, so named by 

 Sir E. Murchison, and described in 

 his Silurian system, has been 

 found in the older rocks. 



Mroco'NCHA. A genus of fossil bi- 

 valve shells, belonging to the 

 Cardiacea ; they are oval, equi- 

 valve, oblique; the umbones are 

 terminal, the hinge has an external 

 ligament, and an oblique elongated 

 tooth in the left valve, the general 

 form of this shell is that of My tilus ; 

 the only known species is the M. 

 Crassa of the Great and Inferior 

 Oolite. 



MTETA'PODA. } (from fivpia, ten thous- 



MY'RIAPODS. ) and, and TTOVS, nodo?, 

 a foot, Gr.) A class of insects, 

 commonly called Centipedes, pos- 

 sessing a number of feet, from six 

 to some hundreds. The Myriapoda, 

 in general, resemble little serpents, 

 or Nereides, their feet being closely 

 approximated to each other through- 



out the whole extent of the body. 

 Myriapods exhibit the following 

 general characters. Animal under- 

 going a metamorphosis by acquir- 

 ing in its progress from the egg to 

 the adult state several additional 

 segments and legs. Body without 

 wings, divided into numerous pedi- 

 gerous segments, with no distinc- 

 tion of trunk and abdomen. Head 

 with a pair of antennae ; two com- 

 pound eyes ; a pair of mandibles ; 

 under-lip connate with the maxillaD. 

 Myriapoda constitutes the second 

 class of the sub-kingdom Annulosa, 

 and comprises two orders, Chilopoda 

 and Chilagnatha. 



MYTILA'CEA. In Cuvier's arrange- 

 ment, the second family of the 

 order Acephala Testacea. All be- 

 longing to this family are bivalves, 

 having a foot which they use in 

 crawling. Mytilacea comprises, 

 in Lamarck's system, Modiola, 

 Mytilus, and Pinna. 



MI'TILUS. (mytilw, Lat.) A genus 

 of the family Mytilacea. The 

 muscle. A rough, longitudinal, 

 bivalve; with equal, convex, anil 

 triangular valves; the anterior, and 

 longest side of the shell, allowing 

 passage of the byssus. The Mytilus 

 is a littoral shell, moored to rocks, 

 stones, crustaceans, &c. The foot 

 of the Mytilus edulis, or common 

 muscle, can be advanced to the 

 distance of two inches from the 

 shell, and applied to any fixed 

 body within that range. By at- 

 taching the point to such body, and 

 retracting the foot, this animal 

 drags its shell towards it ; and by 

 repeating the operation successively 

 on other points of the fixed object, 

 continues slowly to advance. Some 

 Mytili produce pearls. 



