M U S 



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M Y T 



MU'SCLE-BIND. The name given to a stra- 

 tum of imperfect ironstone and indu- 

 rated shell, found in the Derbyshire and 

 Yorkshire coal fields. The shells re- 

 semble fresh-water muscles, and they are 

 most abundant. 



MU'SITE. )A mineral, thus named from 



MU'SSITE. ) Mussa, in Piedmont, where 

 it occurs. It is a white, or pale green, 

 variety of augite. 



MY'A. (from pvwv, a muscle, Gr.) A 

 genus of bivalves belonging to the family 

 Myaria. Animal an ascidia. Shell 

 transverse, oval, thick, gaping at both 

 ends ; ligament internal. Hinge with 

 broad, thick, strong, patulous tooth, sel- 

 dom more than one, perpendicular to the 

 valve, and giving attachment to the liga- 

 ments. The My a is found on beaches, in 

 which it often lies buried, with its tube 

 just projecting. It is found in the sea 

 and in rivers ; principally in the silt of 

 estuaries. It belongs to the northern 

 hemisphere. Whether any shells of this 

 genus have been found fossil appears 

 problematical. Lamarck states that he 

 has not met with any ; Parkinson men- 

 tions that a shell resembling Mya is 

 found in the cliffs at Bognor, but that he 

 is not able to speak decidedly with re- 

 spect to it ; and Dr. Mantell places it 

 among the fossils of the Shanklin sand, 

 but with a note of interrogation. 



MY'LIOBATES. A genus of fossil Rays. 

 They are abundant in the London clay 

 and in the crag. 



MYRIA'METER. (from pvpia, ten thou- 

 sand, and /Lttrpov, measure, Gr.) A 

 French measure, the length of ten thou- 

 sand meters, equivalent to two mean 

 leagues of the old measure. Brongniart 

 has expressed, in strong terms, his im- 

 pression on the subject of the distur- 

 bance of the strata composing the earth's 

 crust, by saying that there is hardly a 

 square myriameter which is left in its 

 original position. 



MYRIA'PODA. ) (from /iwpicr, ten thousand, 



MY'RIAPODS. \ and TTOVQ, Tro^og , a foot, 

 Gr.) A class of insects, commonly called 

 Centipedes, possessing a number of feet, 

 from six to some hundreds. The Myria- 

 poda, in general, resemble little serpents, 

 or Nereides, their feet being closely ap- 

 proximated to each other throughout the 

 whole extent of the body. Myriapods 

 exhibit the following general characters. 

 Animal undergoing a metamorphosis by 



acquiring in its progress from the egg to 

 the adult state several additional seg- 

 ments and legs. Body without wings, 

 divided into numerous pedigerous seg- 

 ments, with no distinction of trunk and 

 abdomen. Head with a pair of an- 

 tennae ; two compound eyes ; a pair of 

 mandibles ; under-lip connate with the 

 maxillae. 



This class is divided into two orders, 

 the Chilognathans and the Chilopodans. 

 The julus terrestris, belonging to the 

 first of these two orders, has, at its 

 entrance into the world, only eight seg- 

 ments and six feet ; but acquires, in the 

 course of its development, fifty segments 

 and about two hundred feet. The an- 

 terior legs are directed obliquely for- 

 wards, and the rest more or less back- 

 wards. The Myriapoda possess in their 

 internal structure an organization closely 

 allied to the larva of insects. 



MYTILA'CEA. In Cuvier's arrangement, 

 the second family of the order Acephala 

 Testacea. All belonging to this family 

 are bivalves, having a foot which they 

 use in crawling. Mytilacea comprises, in 

 Lamarck's system, Modiola, Mytilus, and 

 Pinna. 



MY'TILUS. (mytilus, Lat.) A genus of 

 the family Mytilacea. The muscle. A 

 rough, longitudinal, bivalve ; with equal, 

 convex, and triangular valves ; the an- 

 terior, 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 attach- 

 ing the point to such body, and retract- 

 ing the foot, this animal drags its shell 

 towards it ; and by repeating the opera- 

 tion successively on other points of the 

 fixed object, continues slowly to advance. 

 Some Mytili produce pearls. 



Lamarck describes two species of fos- 

 sil Mytili, found at Grignon and Long- 

 jumeau. Dr. Woodward mentions se- 

 veral shells of this genus found fossil in 

 different parts of England ; and Dr. Man- 

 tell states that they are found in the 

 Ashburnham beds ; in the lower green 

 sand ; and in the diluvium of Sussex. 

 Dr. Mantell also states that shells of this 

 genus were found by himself and Mr. 

 Lyell in a bed of shale. 



