MOKFHOLOGY OF LAMELIJISKAXCHIATE MOLLU.SKS. 431 



Plate LXXXII— L'outiuued. 



f'ciius mercvuaria — Quuhoij — Cou tinned. 



Fig. 18. Same, iu regiou of middle of posterior adductor, pa; m, tliickeuod luusciilar mantle ed>'e; 

 ws, lower wall of brauchial siphouseea posterior to braucbial membrane, hvm. ('I'hi.s repre- 

 sents tbe anterior surface of tbe section.^ 



FKt. 19. Saiue, in reftiim of base of siphon. »s\ up})er or ;inal siphon; /s. lower or brauchial siphon : 

 ./■, point where branchial siphon remains continuous with mantle; m. mantle coutinucil 

 across below siphons; -s'.s, siphonal se])tnm. 



Fi<;. 20. Same, just posterior to last. Siphons still bcueath posterior adductor, ;>«, stiparated from 

 mantle, which is yet continuous beneath them. 



Fk;. I'l. Same, posterior to last, mantle not continuous beneath siphons. Lnmtm of branchial 

 siphon, Is, assumes oval outline. 



Fk;. 22. Same, through free siphons. 

 Mija aienaria — Long clam : 



Fiu. 23. Vertical, transverse section iu region of anterior adductor, «; inv, thick mantle edge; r, 

 cuticle from mautle edge; in, mantle below adductor; branchial chamber closed in bv con- 

 crescence of mantle edges below ; /', foot much flattened laterally. 



Plate LXXXIII. 



Mya arenaria — Long clam : 



Fig. 24:. Vertical, ti'ausverse section in regiou of anterior end of visceral mass; me. mantle edo-e; 

 oe, thick-walled (cso])hagus; o^j, onter palp ; ip, inner palp; »>i. mantle; </, generative mass; 

 I, liver. 



Fitr. 25. Same, in regiou of anterior end of stomach, s; /.^, inner gill; o(/, outer gill; cc, epibranchial 

 chamber; i. intestine; est, crystalline style ruuning forward on ventral side of abdomen. 



Fkj. 26. Same, in region of posterior end of stomach; bv. blood vessel; est, crystalline style, orig- 

 inating from ventral wall of stomach, .s, and running on right side of body to bottom of 

 visceral mass. It then turns forward, and is shown iu section in the preceding figure. 



Fkt. 27. Same, in regiou of heart, /t; «, uephidium: oL outer lamella of outer gill; Hi/', muscle Hbers 

 in generative gland. 



l'i(i. '2H. Diagram to show plane of sections through folded gills of Mga and Vcnux. explainiu"- 

 reason of folded appearance in vertical sections of the whole animal. 



Fiti. 29. Section just anterior to base of siphons, the anterior face of section; r. rectum, below 

 plane of section, opening into continuation of epibranchial or the cloacal chamber, cl ; gl. 

 outer lamella of gill in concrescence with mantle, (rills here form complete septum between 

 branchial and c|iibranchial chambers; bs, base of brauchial siphon below plane of section; 

 irs, siphonal walls; brni., fold at anterior end of siphonal septum, probably representing 

 branchial membrane of Venus, Mactra, etc. ; ct. jelly-like layer, clothing posterior end of 

 mantle and extending out over siphon.s. 



Fi(i. 80. Same, through base of siphons, right side cut a little deeper than left. The thickened 

 mantle walls, ws, in the previous tigures, become here the siphonal walls, ws, and are now 

 much thicker; cl. upper end of (doaca opening below into anal siphon, us; ss, siphonal 

 septum. 



Fk;. 81. Same, through siphons at ;i distaucc from mantle; ?»c, blood vessel. A similar vessel is 

 present above the anal siiihou. 

 Mtitihis ('(IhUs — Common mussel: 



Fu;. 32. Transverse, vertical section through anterior end of liody ; /, liver mass; og, outer gill; ig, 

 inner gill; /**, thickened mantle, contaiuiug sexual gbiud. That portion (m the median line 

 has been drawn in greatly on killing, and thus api)ears iu section; ar, anterior retractor ; 

 pi, palp; aa. anterior adductor; me, mautle edge. 



