Bull. U. S. B. F., 1921-22. (Doc. 922.) 



LR' \Liq 



102 y 



PRct PAd 



AR< 



An 



Aj\cI 



104 'Pal 



Fig. 102— Interior view of hince ligament. Lig, ligament; LR, ligament ridge 

 FlG. 103. — Interior view of anterior end of a valve showing four hinge teeth, T. 

 Fig. 104. — Inner surface of a valve showing muscle impressions. .1.1/. anterior adductor 

 muscle; An, anal muscle; A Ret, anterior retractor muscle; PAJ, posterior adductor muscle; Pal 

 pallial muscle; PRet, posterior retractor muscle. 

 Fir.. 105.— Dorsal surface of a shell from which periostracum and ligament have been removed. 



LC, ligament cleft. 

 Fig. 106. — Ventral surface of a shell from which periostracum has been removed. ByC, byssus 



cleft; I.n. lunula. 



