MAC 



[270] 



MAC 



lead to an octohedron for their 

 primitive form. Made scratches 

 glass ; its powder is soft and unc- 

 tuous. It is opaque, or sometimes 

 translucent. Colour, white or gray, 

 often shaded with yellow, green, or 

 red. Specific gravity 2*94. It is 

 found, generally, imbedded in 

 black argillaceous slate. 



MACLT/EEA. A genus of fossils of the 

 Silurian formation. 



MACLU'EEITE. Called also Brucite 

 and Chondrodite. A mineral occur- 

 ring in imbedded grains in small 

 massive pieces, and in longish 

 granular concretions. Colours yel- 

 low, straw-colour, orange, red, and 

 brown ; translucent ; scratches 

 glass ; fracture imperfectly con- 

 choidal. Specific gravity 3-15 to 

 3*50. It consists of magnesia 54*0, 

 silica 36-60, fluoric acid 4-0, oxide 

 of iron 2*30, potash 2-0, manganese 

 a trace. 



MACEOPO'MA. The name given by M. 

 Agassiz to a genus of sauroid fishes, 

 the fossil remains of which have 

 been discovered in the chalk for- 

 mation. The scales of the Macro- 

 poma are studded with hollow 

 tubes, through which, it is stated, 

 there flowed a fluid which served 

 to lubricate the surface of the 

 body. 



MACEODA'CTYLTJS. (from fuucpo?, long, 

 and ^aKTvXos, finger, Gr.) The 

 name given to a family of birds in 

 Cuvier's arrangement, having very 

 long toes. The coot, rail, &c., are 

 examples. 



MA'CEODON. (Lycett.} Figure resem- 

 bling Byosoarca, with a similar 

 aperture in the lower border; 

 several teeth placed at the anterior 

 extremity of the hinge plate are 

 parallel and directed obliquely 

 downwards and backwards ; one or 

 two elongated teeth or plaits, 

 occupy the length of the hinge 

 plates. Macrodon Hirsonensis oc- 

 curs in the great and inferior oolite 

 of the Cotteswolds. 



MACEOSPO'NDYLTJS. A fossil saurian 

 found in the oolite and lias forma- 

 tions. 



MACEOSTO'MATA. (from /ta/^os, long, 

 and <7To/ta, mouth, Gr.) A family 

 of univalves, belonging to the order 

 Trachellipoda, comprising the gen- 

 era Stomata, Stomatella, and 

 Haliotis. 



MACEOT/EA. (from [icucos, long, and 

 ovpa, a tail.) A family of crus- 

 taceans, including the lobster, 

 prawn, shrimp, &c. They are so 

 named from their having a long 

 tail, which is, at least, as long as 

 the body, and provided at its termi- 

 nation with appendages which 

 most frequently form a fin on each 

 side. This tail is always com- 

 posed of seven distinct segments. 

 Fossil genera of the family Ma- 

 croura have been found in the 

 Muschelkalk and in the lias. 



MA'CTEA. (/xaKT/>a, Gr. mactra, Lat. 

 a kneading-trough.) A genus of 

 equivalve, inequilateral, transverse 

 bivalves, slightly gaping at the 

 extremities; the hinge, or middle 

 tooth, complicated ; lateral teeth 

 rather remote, compressed, and in- 

 serted. Shells of this genus have 

 only been found to inhabit the 

 ocean, at depths varying from ten 

 to twelve fathoms, in sands and 

 sandy mud. The French natural- 

 ists divide Mactra into two genera, 

 Mactra and Lutraria. In Turton's 

 Linne twenty- seven species are de- 

 scribed ; twelve are inhabitants of 

 our seas. The fossil species belong 

 to the tertiary formations. 



MACTEOMY'A. A genus of fossil 

 bivalve shells found in the Jurassic 

 rocks, they are equivalve, rather 

 globose and rugose ; the hinge is 

 without teeth, on the posterior 

 side of the umbo is an hiatus 

 surrounded by a thickened laminal 

 plate to support the ligament. Qne 

 species occurs in the Lias, two in 

 the Inferior and Great Oolite in 

 England. Lycett. 



