MORPHOLOGY OF LAMELLIBRANCHIATE MOLLUSKS. 435 



Plate XCI. 

 Solenomya velum : 



Fig. 77. Cross-sectiou of two gill plates; (/le, glaud colls; ve, ciliated, columnar cells of thickeuod 



ventral edge of plate ; ch, chitinous rods, lined interiorly by endothelium ; iv, cells of interior 



walls of plate. 

 Yoldia Umntuht : 



Fig. 78. Diagrammatic view of ventral edges of gill jdates; p, ventral edges of plates ; (jr, ventral 



groove; cj, ciliated junction between plates. 

 Fig. 79. Vertical section across gill plate ; e, frontal epithelium bearing very large cilia ; r, ridge of 



cells forming first compound straining line ; /, cells forming second compound straining line ; 



ch, cliitin, inclosing b, a blood-channel lined by endothelial cells; s, blood space of interior 



of plate, bridged across by numerous branching lacunar cells, lac; f, folds in wall of plate; 



d, blood space at dorsal edge of plate. 

 Fig. 80. Cross-section of dorsal ends of plates of gill; lac, numerous lacunar cells; ep, epitlielium 



on surface of supporting membrane of gills; m, muscles of same. 

 Fig. 81. Diagram of plates of gills showing planes of sections; a, plane of Fig. 79; h, of Fig. 82; 



c, of Fig. 80; d, of Fig. 48, PI. lxxxvi. 

 Fig. 82. Sections of plates of gill, Yoldia, in plane /, Fig. 81, showing lines of ciliated junction, 



c/; e, lateral edge of plates; s, space between edges of plates where ciliation is absent; lac, 



lacunar tissue; ep^ epithelium of supporting membrane of gills; m, muscles of same. 



Plate XCII. 



Pecten irradians — Scallop : 



Fig. 83. Cross-section of single filament, gill of Pec<e«; /, ciliated frontal epithelium; f/Zc, gland 

 "* cells; ijg, pigment in region of gland cells; If I, cells of compound straining line; ch, chitin; 



p, 8ep:um of filament showing nucleus. 

 Fig. 84. Diagram of portions of three filaments of gill, to show nature of ciliated spurs, cs, which 

 form means of interfilamentar union; fil, filament. 

 Anoinia sinn)Iex : 



Fig. 85. Inner ends of filaments of Anomia, to show gland cells. 

 Pecten irradians — Scallop : 



Fig. 86. Cross-section of gill of Pecten ; ra, reentering angle of gill folds ; sa, filament at salient 

 angle of gill fold ; ch, chitin of modified filament of reentering angle ; If I, straining line of 

 modified filament ; be, blood space of modified filament ; tv, walls of modified filament, 

 forming interlamellar union ; lac, lacunar tissues ; es, ciliated spurs connecting filaments. 



Plate XCIII. 



Mytilus ednlis — Common mussel : 



Fig. 87. Siphonal region of mantle in JfyfiZws seen from behind; co, cloacal opening ; brm, branchial 



membrane; me, mantle edge. 

 Fig. 88. Same, seen from in front; co, cloacal opening; o(j, outer gill; brm, branchial membrane; 

 m, mantle. 

 Ostrea virginiana — Oyster : 



Fig. 89. Posterior region of mantle in Ostrea, seen from behind; r, rectum, opening into upper end 

 of cloacal chamber; brp, concrescence of mantle edges above gills; ig, inner gill; og, outer 

 gill ; me, mantle edge. 

 Venus mercenaria — Quahog : 



Fig. 90. Posterior region of mantle in Venus, view of base of siphons; og, outer giU; bm, branchial 

 membrane ; me, mantle edge. 

 Solenomya velum : 



Fig. 91. Gills of one side of body in Solenomya; m, supporting membrane; gr, groove on median 

 line opposite supporting membrane. 

 Yoldia limatula : 



Fig. 92. Gills of one side of body in Yoldia; m, supporting membrane; gr, groove on midline of 

 ventral surface. 



