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THE NAIADES OF MISSOURI 



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. 



Fio. 6. Lastena suhurbicidata (Say) 9. Diagram of a gravid individual 



from Lake Contrary, St. Joseph, showing animal characters 



in left valve. {% nat. size.) 



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 spadijorm, 

 hinge line straight, longer than high, {0.325 x 0.320mm.) glochidial 

 shell russet color, bluish spots jor the adductors; no conglutinates 



