NAIADES OF MISSOURI I51 
septa closely crowded, when charged distended very little even in 
median-longitudinal line, ventral edge not blunt, ovisacs rather 
narrow; conglutinates white, narrowly lanceolate, not solid; 
glochidia large, spineless, ventral margin rounded, hinge line short, 
straight, or nearly so, measures 0.267 x 0.325mm., collected by author, 
Aug. I1, 1913, Osage River, Bagnell, Missouri. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell oval quadrate, medium in 
size, compressed, heavy, thick, rounded in front, usually emargi- 
nated post-dorsad with radial furrow from this sulcation to beaks, 
dorsal ridge rather high with upcurved costae; post-umbonal 
ridge rather rounded; posterior half of shell profusely sculptured 
with coarse pustules and fine tubercles; umbones low, pitched 
considerable anteriorly, sculptured with numerous, heavy, wavy 
‘or corrugated ridges which extend down on upper part S disk; 
epidermis brownish red to black. 
INTERNAL STRUCTURES:—-Cardinals double in left, rather 
tripartite in right valve; laterals double in both valves, lower 
right lateral rudimentary, scars deep; beak cavities very deep 
antero-postero, narrow diametrically, wide vertically, nacre 
rich purple, with part within the mantle line a lighter shade, 
sometimes whole nacreous surface faded to whitish with pinkish 
teeth. 
Sex Length Height Diameter U. ra. Locality. 
@ 80 x 60 x 37mm 0.120 (Meramec R., Fern: Glen) 
Cu OA XS 5A ee eT! 0.135 (Gasconade R., Gascondy) 
OPO ZN XU NO2 "oxi sary 0.128 (Osage R., Schell City) 
The last measurement is that of the smallest juvenile out of 
a collection of 156 collected in a space twenty-feet square in the 
White River. This place was a quiet retreat of shallow water with 
a thin coating of mud over a substratum of limestone. 
MISCELLANEOUS REMARKS:—The peculiar shell characters 
of this species in being suborbicular, heavy, with low corrugated 
beaks and the unique anatomical characters in possessing no 
supra-anal opening and only outer gills as marsupial are features 
especially to be noted. Its distribution in this state is peculiar 
in that it is not found at all in the interior northern drainage of 
the Mississippi River, and is confined in its typical form more. in 
the drainage of the south slope of the Ozarks and in the Missouri | 
portion of the Mississippi while it occurs by intergrades in the 
