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THE NAIADES OF MISSOURI 257 
soft parts; gills olivaceous; patch in front of branchial opening 
light tan or chamois-like; cerebral ganglia bright orange spots 
external and on top of foot antero-ventrad to palps. 
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Fic. 6. Lastena suborbiculata (Say) 9. Diagram of a gravid individual 
from Lake Contrary, St. Joseph, showing animal characters 
in left valve. (34 nat. size.) 
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REPRODUCTIVE STRUCTURES:—Marsupia when sterile, dark 
tan with crowded septa, tissue of ventral edge thickened, occupying 
outer gills only; when gravid, russet, with heavy septa more widely 
separated, distinct, veining enormously pad-like, greatly dis- 
tended and faintly scalloped ventrad, longitudinal line, near and 
parallel to the ventral margin, indicating terminations of gill 
filaments; water canals next to thin laminae on either side of an 
undivided central ovisac which is closed at the base; no sexual 
specialization on margin of mantle antero-ventral to branchial 
opening (thickened edges here have nutritive function of siphonal 
contraction); glochidium spined, very large, broadly spadiform, 
hinge line straight, longer than high, (0.325 x 0.320mm.) glochidial 
shell russet color, bluish spots for the adductors; no conglutinates 
