49 



CHAPTER VII. 



OF THE MYA. GENUS IV. 



MY A. 



"Animal an Ascidia. Shell bivalve, open at one end ; the hinge with a tooth, 

 (in many) solid ; thick, spreading, and hollowed (not inserted in the oppo- 

 site valve)." — Linn. 



Most of these shells have a large perpendicular projection in 

 one valve, called a tooth by Linnaeus (yj/. 1. /. 10. a), slightly 

 hollowed for holding the cartilage ; but it has no teeth like 

 those of the other genera, as Tellina, Venus, or Cardium ; the 

 other valve has a hollow under the beak that receives the 

 opposite side of the cartilage, as in M. arenaria and trun- 

 cata. These shells are unable to shut close at one end : the 

 cartilage is wholly internal in the hollows before mentioned. 



The animal is nearly similar to the animal of the Pholas ; 

 some species are capable of extending their tubes to the length 

 of eight or nine inches, and which are united their whole 

 length, like the Pholas ; the mantle is closed in front, and it 

 protrudes a short foot from the lower end. Some species are 

 only capable of contracting their tubes to about three inches 

 in length, but cannot withdraw them completely within the 

 shell. 



They are generally found buried in the sand of the sea 

 shore, at such depths that they can just reach the surface with 



II 



