THE NAIADES OF MISSOURI 1 73 



ANIMAL CHARACTERS. 



Nutritive Structures: — Branchial opening large with large 

 yellowish papillae; anal crenulated; supra-anal moderately 

 separated from anal by distinct mantle connection; gills wide, the 

 inner slightly longer and wider, the inner laminae connected with 

 the visceral mass their entire length; palpi wide and large, united 

 one fourth of their length antero-dorsad ; color of soft parts tan- 

 color except foot which is more yellowish and mantle edge which is 

 black for the siphonal openings. 



Reproductive Structures: — ^Marsupia wide, more or less 

 reniform, consisting of about a dozen large distinct ovisacs, dis- 

 tended, when gravid, transversely in center and along the ventral 

 edge into black pigmented beads at the distal ends; conglutinates 

 white, rather club-shaped; glochidia moderately large, semi-elliptical, 

 hinge line slightly oblique and undnlate measuring o.2joxo.jOj mm.; 

 mantle edge antero-ventrad to branchial opening with a flap 

 extending toward the center of ventral margin with about ten 

 papillae beginning rather low at edge of branchial opening and 

 ending with tentacular processes at end. 



SHELL CHARACTERS. 



External Structures: — Shell medium in size, thick to thin, 

 subelliptical ; post-umbonal ridge lacking; beaks large but low- 

 sculptured b)" six inverted V-shaped ridges the posterior ones 

 being longer and thrown more or less obliquely across post-umbonal 

 slope; disk without sculpture; male shell rounded before, rounded 

 and more or less biangulated behind ; female shell very deeply and 

 widely sulcated at the post-ventral margin of shell and is less 

 elliptic in general outline, also thicker and more inflated than 

 male shell; epidermis yellow to olivaceous with broad, widely 

 separated rays of interrupted lunate or V-shaped splotches — all 

 covering the whole shell. 



Internal Structures: — Cardinals stout, double in left, 

 single in right valve; interdentum long, narrow; laterals short 

 somewhat curved reaching far back; beak and branchial cavities 

 rather deep and basin-like; scars well impressed; nacre white, 

 pinkish and irridescent posteriorly. 



Sex Length Height Diameter Locality 



9 64 X 40 X 27mm — (Niangua R., Hahatonka ) 



9 55 X 36 X 25mm — ( " " , " ) 



cf" 40 X 24 X 14mm — ( " " " ) 



