318 MARINE INVERTEBRATES 
7:770.€. 
Ideal or schematic mollusk. 
1, dorsal view: h, head; t, cephalic tentacle; sh., shell covering visceral mass; b. m., outline of 
body-mass; 7. m.e., edge of mantle; c.t., ctenidia, or gills; g.a., generative apertures; r.e., renal 
openings ; ¢. 0., excretory opening; f, posterior portion of foot; 0. e. m., edge of shell. 
2, ventral view: h, head; t, tentacle; m, mouth; b, outline of body; e.m., edge of mantle; s./., 
lower surface of foot; ¢. t., ctenidia, or gills; Jf, posterior portion of foot. 
3, horizontal section, showing heart, nephridia, and gonads: m, mouth; 0, esophagus; g, gonad; 
Pp, pericardium; n, nephridium, or renal organ; v, ventricle; a, auricles; g’, gonad aperture; n', 
renal opening; e, excretory opening; j, posterior portion of foot. 
4, vertical median section: m, mouth; b.m., buccal mass; 1, liver; d.a@., digestive tract; gq, 
gonad; /, foot; g.0., gonad aperture, or opening of oviduct; 7. 0., renal opening; ¢.0., end of diges- 
tive tract, excretory opening; n, mantle; r, nephridium, or renal organ; 0. /., recurved portion of 
mantle; sh., shell; v, ventricle; p, pericardium. 
