220 



POPULAR CONCHOLOGY. 



aria) and those having two (Dimyaria). In this distribu- 

 tion all regard to their powers of locomotion is lost sight of, 

 and an arrangement of the families according to their 

 degrees of perfection becomes impossible. 



Notwithstanding the above remark, the Conchifera are 

 still arranged by the two well known orders of Dimyaria 

 (or those having two fastening or adductor muscles) and 

 Monomyaria with only one, Philippi adding another be- 

 tween the two, Heteromyaria, including those still having 

 two muscular impressions, but which are at unequal dis- 

 tances from the edge. 



Order I. 



DIMYARIA. 



The animals of this order have two nearly equal adductor 

 or fastening muscles ; the shells therefore have two muscu- 

 lar impressions in each valve, which are generally dis- 

 tinctly visible. 



Family 1.— TELLINACEA. 



The animal has the two lobes of the mantle separated 

 (where the valves open) in their entire length, and pro- 

 longed behind into two either long or short tubes; the 

 foot is compressed, generally tongue- shaped, never pro- 

 ducing a byssus ; the gills are four, and leaf-shaped. The 

 shell is tolerably equivalve, the hinge has several cardinal, 

 and sometimes lateral teeth. The marine genera are 



