FAMILY 5. MACTRACEA. 01 



MACTRA, Linnaeus. 



Testa aequivalvis, subaequilateralis, plerumque trigona, lateribus paulu- 

 liim hians ; dente cardinali trigono in utraque valva. cum foveola 

 adjecta ; dentibus lateralibus in valva altera, duobus anticis, duobus 

 posticis ; in altera, uno antico, uno postico. Ligamentum duplex, 

 majus internum. 



The Mactrae are very numerous, and include many rare and beautiful 

 species ; their shells exhibit rather a diversity of form, but are generally 

 more or less triangular. 



They are described as being equivalve, nearly equilateral, and gene- 

 rally gaping a little at the sides. The hinge is characterized by a pro- 

 jecting triangular cardinal tooth in each valve, with sometimes another 

 thin sharp one on the posterior side of it ; there is also an elongated 

 lateral tooth diverging from each side the umbo in one valve, fitting 

 between two similarly situated in the opposite valve. The ligament is 

 duplex, mostly internal, inserted in a deep pit between the triangular 

 cardinal teeth. 



Examples. 



PI. XIII. Fig. 1. 

 Mactra Spengleri, Gmelin, Syst. Nat., p. 3256. Lamarck, Anim. sans 



vert., new edit., vol. vi. p. 97. Enc. Meth., pi. 252. f. 3. 

 Schizodesma Spengleri, Gray. 



PI. XLII. Fig. 2. 

 Mactra turgida, Gmelin, No. 17. Lamarck, Anim. sans vert., new 

 edit., vol. vi. p 102. Enc. Meth., pi. 255. f. 3. 



PI. XLII. Fig. 3. 

 Mactra solida, Linnaeus, Syst. Nat., p. 1126. Lamarck, Anim. sans 

 vert., new edit., vol. vi. p. 104. Enc. Meth., pi. 258. f. 1. 



