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



PAd PRet L ARet 



An 



Fm. M Mes < I IhiR Ft LP 

 117 9 



Mlli 



-OLP 

 ILP 



PAd 



--BrM 



-Exs 



-BrM 



' Ins 



FlG. 115. — Dorsal view of an adult mussel w ith valves open normally. 



Fig. i 16. — Dorsolateral view of an adult mussel from which shell has heen removed. 



FlG. 117. — Median view of a mussel with right valve, ri^ht mantle lobe, and gills rem<n ed, 



FlG. i iS. — Ventral interior view of a mussel with anterior and posterior muscles cut and valves laid open. 



Abbreviations.— An, anal muscle; ARet, anterior retractor muscle; lower BrM in. fig. 115, main portion of branchial 

 membrane, upper BrM in fig. 115 and BtM in fig. 116, extension of branchial membrane; ByR, hyssus root bearing 

 threads; ByP, hyssus pit; ExS and Exs, exhalcnt syphon; Fm, fimbriie of mantle; Ft, foot; IBr, inner branchial fold; 

 /LP, inner labial palp; InS. inhalent syphon; /,, liver; LP, labial palp; M, mantle; Mes, mesosoma; Mth, mouth; OBr, 

 outer branchial lamella; OLP, outer labial palp; PAd, posterior adductor muscle; Pal, pallial muscles; PIC, plicate 

 canals; PRet, posterior retractor muscle; 5, sucker; V(Jr, ventral groove. 



