CLASS IX. ORDER III. 115 



bent lips ; hinge with three teeth, all of them ap- 

 proximate, the lateral ones divergent at the tip. 



SPONDYLUS, (thorney oyster,) animal a tethys ; 

 shell hard, solid, with unequal valves ; one con- 

 vex, the other rather flat ; hinge with two recurv- 

 ed teeth separated by a small hollow. 



CHAMA, (basin conk,) animal a tethys ; shell 

 bivalve, rather coarse ; hinge with a callose gib- 

 bosity, obliquely inserted- in an oblique hollow 

 anterior slope closed. 



ARCA, (noah's ark,) animal a tethys ? shell bi- 

 valve, equivalve ; hinge with numerous sharp 

 teeth alternately inserted between each other. 



OSTRBA, (oyster, scallop,) animal, a tefchys ; 

 shell bivalve, generally with unequal valves and 

 slightly eared ; hinge without teeth, but furnished 

 with an ovate hollow, and mostly lateral, trans- 

 verse groove. 



ANOMIA, (thin-shell,) animal emarginate, cili- 

 ate, strap-form, with bristles or fringe affixed to 

 upper valve ; shell bivalve, one valve flatish, the 

 other gibbose at the base, with a produced beak 

 generally curved over the hinge ; hinge without 

 teeth, but a lateral tooth within, on the margin of 

 the flat valve ; two bony rays for the base of the 

 animal. 



MYTILUS, (mother pearl, muscle.) animal al- 

 lied to an ascidia ; shell bivalve, rough, generally 

 affixed by a byssus or beard, of silky filaments ; 

 hinge mostly without teeth, with sometimes a su- 

 bulate excavated longitudinal line. 



PINNA, (wing-clam,) animal a limax ; shell 

 sub-bivalve, fragile, upright, gaping at one end, 

 and furnished with a bissus ot beard ; hinge with- 



