XI 



PHYLUM MOLLUSCA 



267 



of the mantle : the streak is hence called the pallial line, 

 Beneath the anterior end of the hinge the pallial line ends in 

 an oval mark, the anterior adductor impression (a.ad.), into 



7i.L 



a ad. 



FIG. 147. Anodonta cygnea. A, interior of right valve ; B, the animal removed 

 from the shell, a. ad. anterior adductor or its impression ; a. r. anterior re- 

 tractor or its impression; d.gl. digestive gland, seen through mantle; ex.sph. 

 exhalant siphon ; ft. foot ; gl. gills, seen through mantle ; /;. /. hinge-line ; 

 in. sph. inhalant siphon ; kit. kidney, seen through mantle ; k. o. Keber's organ, 

 seen through mantle ; m. mantle ; /. ad. posterior adductor or its impression ; 

 pc. pericardium, seen through mantle ; //. /. pallial line ; //. w. pallial muscles ; 

 /. r. posterior retractor or its impression ; prc. protractor or its impression. 



which is inserted one of the muscles which close the shell. 

 A similar, but larger, posterior adductor impression (p. ad.) lies 

 beneath the posterior end of the hinge. 



