436 THE AMERICAN MIDLAND NATURALIST 
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 undulate measuring 0.250X0.305 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 by 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 ) 
OM WS 5e x) ZO) ox, 2s —— (eee uP i ) 
OsAO} X “24° 2x > w4amm——( 9 ve ” by ) 
