NAIADES OF MISSOURI 27 



ANIMAL CHARACTERS. 



Nutritive Structures: — Branchial opening with papillae on 

 inner edge, anal with fine but distinct papillae; supra-anal long 

 and large with very short connection of mantle edge; gills sharply- 

 pointed behind with wide space between the anterior attachment 

 to mantle and base of the palpi, inner laminae of the inner gills 

 entirely free from visceral mass; palpi rather large, subfalcate; 

 color of soft parts variable, but usually orange yellow especially 

 the distal end of foot, also mantle edge and adductors, while sterile 

 gills are brownish. 



Reproductive Structures: — Marsupia with crowded septa 

 dividing the ovisacs parallel to the gill filaments; when charged, 

 lumen of ovisacs somewhat cylindrical containing club-shaped 

 conglutinates which are carmine red or pinkish to whitish in 

 color; glochidia somewhat small, semicircular, spineless, hinge 

 line nearly straight, about as long as high (0.150 x 0.15.5mm). 



SHELL CHARACTERS. 



External Structures: — Shell trigonal-quadrate, rather 

 thick, compressed, rather rounded post-dorsad, gently curved 

 ventrad; disk somewhat undulated by growth lines; beaks not 

 very high or full, sculptured by concentric ridges breaking into 2 

 or 3 nodules at base of posterior ridge; this post-umbonal ridge 

 usually flattened; epidermis yellowish to dark horn color, rayed 

 in well preserved and young shells, eradiate in old. 



Internal Structures :— Cardinals double in both valves; 

 laterals long, serrated; scars well impressed; beak cavity narrowly 

 deep; nacre mostly white, sometimes tinged with salmon in beak 

 and antero-branchial cavities, irridescent. 



Length Width Diameter Locality. 



65 X 45 X 30mm (St. Francis River, Greensville, Mo.) 



43 X 35 X 25mm ( 



50 X 40 X 24mm (White River, HoUister, Mo.) 



34 X 27 X i6mra ( " " " " ) 



This latter measurement is that of a somewhat advanced 

 adolescent shell. However, it shows the juvenile characters of 

 a flattened post-umbonal ridge, a rounded post-dorsal line and the 

 very distinct concentric sculpturing on the beaks much more 

 evidently than in the adult. The most striking characters, that 

 are absent in the mature shell, are the green rays. 



