7 



-b-yi 



THE NAIADES OF MISSOURI I39 



to yellowish, generally with very distinct green rays; sex dimor- I 



phism of shell not well shown. 



Miscellaneous Remarks: — ^This genus is set aside solely \ /•.'>'' 

 on shell characters. The sub-genus, Pseudoon, serves as a good ' 



connecting link between Ohovaria and Nephronaias. Chiefly 

 because of the lack of much specialization of the mantle border 

 antero-ventrad to the branchial opening Unio ligam'entina (Lam.) 

 is taken out of Simpson's grouping of it as a Lampsilis. In this 

 State this genus is best represented by N. liganientina and ellipsi- 

 jormis (Lea). 



Nephronaias ligamentina (Lamarck). /' 



PI. XXV, Figs. 85 A and B. 

 1 8 19 — Unio ligamentina Lamarck, An. San. Vert., VI, p. 72. 

 1900 — Lampsilis ligamentina Simpson, Proc. U. S. Nat. Mus., XXII, 

 P- 539- 



1912b — Nephronaias ligamentina (Lam.) Ortmann, An. Car. Mus., 

 VIII, p. 325. 



ANIMAL CHARACTERS. 



Nutritive Characters: — Branchial opening large with strong 

 papillae; anal distinctly crenulated; supra-anal rather small, 

 well separated from anal by thick mantle connection; gills very 

 large, inner laminae of inner gills entirely connected to visceral 

 mass; palpi very large, wide and pointed; color of soft parts 

 dingy white for most part, however, post-mantle edge brownish. 



Reproductive Structures: — Marsupia occupying most of 

 outer gills, consisting of about sixty ovisacs well separated by 

 thick septa, when gravid extending far below original edge of 

 sterile marsupium, making a longitudinal line; mantle edge 

 antero-ventrad to branchial opening with twenty-five or thirty 

 low denticulations ; conglutinates white, broad, leaf-like, solid 

 when ova are present, cohesion lost when mature glochidia are 

 developed; glochidia semi-elliptical, spineless, large, hinge line 

 undulate, measures 0.220 x 0.260mm. 



SHELL characters. 



External Structures: — Shell rather evenly eliptical, solid, 

 moderately inflated, beaks rather low, sculpture consisting of 

 several fine, wavy, concentric lines most pronounced at foot of 

 posterior and anterior slopes; disk smooth; epidermis brown or 

 yellowish with broad, dark-green rays. 



