436 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



Plate XCTII — Contmuetl. 

 Venus mercenaria — Quahog : 



Fig. 93. Longitudinal vertical section through posterior mantle region, Feniis; pa, posterior 

 adductor; r, rectum; cl, cloacal region; epo, epibranchial chamber; ig, inner gill; hrm, 

 branchial membrane; h7-c, branchial chamber; me, mantle edge. 

 Mya arenaria — Long clam : 



Fig. 94. Longitudinal, vertical section of posterior mantle region in Mya ; j9«, posterior adductor ; 

 r, rectum; cs, cloacal siphon; bs, branchial siphon; brm, fold in position of branchial mem- 

 brane of Venus; ig, iimer gill; brc, branchial chamber; we, mantle edge; s/,folds in wall of 

 partly contracted siphon. 

 Mytilus edulis — Common mussel : 



Fig. 95. Anterior end of body of Mytilus, cut off by vertical transverse section just behind mouth, 

 to show position of palps; ar, anterior retractor muscles; ip, inner palp; oj>, outer palp; ig, 

 inner gill; m, mantle; mo, mouth. 



Plate XCIV. 



Venus mercenaria — Quahog : 



Fig. 96. Venus, life size, right valve of shell and mantle fold being removed ; aa, anterior adductor 

 muscle; pa, posterior adductor; afr, anterior foot-retractor muscle; pfr, posterior foot- 

 retractor; Ig, ligament of shell; hg, hinge of shell; epc, epibranchial chamber; /(, heart seen 

 beneath; pi, anterior palp; /, foot; me, mantle edge; ig, inner gill; su, portion of mantle 

 remaining on sides of bases of siphons. 



Ostrea virginiana — Oyster : 



Fig. 97. Ostrea, life size, right valve of shell and mantle fold being removed ; Ig, ligament of shell ; 

 ip, inner palp; ig, inner gill; h, nephridium under the adductor muscle; me, mantle etfge; 

 c, cloacal region ; r, rectum ; a, adductor muscle ; /(, heart seen beneath the pericardium. 



