436 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Plate XCIII — Continued. 
Venus mercenaria — Quahog : 
Fig. 93. Longitudinal vertical section through posterior mantle region, Venus-, pa, posterior 
adductor; r, rectum; cl, cloacal region; epc, epibranchial chamber; ig, inner gill; brm, 
branchial membrane; l)rc, branchial chamber; me, mantle edge. 
My a arenaria — Long clam : 
Fig. 94. Longitudinal, vertical section of posterior mantle region in My a ; pa, posterior adductor ; 
r, rectum; cs, cloacal siphon; bs, branchial siphon; brm, fold in position of branchial mem- 
brane of Venus; ig, inner gill; bre, branchial chamber; me, mantle edge; sf, 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 ; op, outer palp ; ig, 
inner gill; m, mantle; mo, mouth. 
Plate XCIY. 
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; h, heart seen 
beneath; pi, anterior palp; f, 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; n, nephridium under the adductor muscle; me, mantle edge; 
c, cloacal region ; r, rectum; a, adductor muscle ; h, heart seen beneath the pericardium. 
