Pio #),") THE AMERICAN MIDLAND NATURALIST 
MISCELLANEOUS REMARKS:—This species is distinguished 
mostly from F. undata and the intergrades by its more quadrate 
and compressed form of shell, by lower beaks, and less upright 
position. /’. undata trigonoides is separated from it by possessing 
a heavier and more elongated shell with a more prominent post- 
umbonal ridge and black epidermis. ‘The White River shells, 
indicated in the above measurements, are rather intergrades 
for this species and hebetata and the St. Francis flava are too 
inflated to be very typical. Since this State proves to be such 
grounds for the inconstant occurence of types, and this species 
is so susceptible to intergradation, it is difficult to find a typical 
flava, such as found in the Interior Basin east of the Mississippi. 
Perhaps its nearest form is in drainage for the south slope of the 
Ozarks in this state, although Simpson reports it as having a 
general distribution throughout the Mississippi drainage. This 
distribution doubtless included its many forms. Simpson further 
states that the St. Lawrence River system includes flava. Dr. Sterki 
(1898, p. 30) considers this species as occasionally hermaphroditic 
by examination of its gonads. Surely this finding can be confirmed 
by the forms of Missouri, for it is rarely that itis even locally a gono- 
chorist. Flava is typically tachytictic being only found gravid 
from May until August. 
Fusconaia hebetata (Conrad). 
Pl. XV ,—Figs. 33A and B. 
1854— Unto hebetatus Conrad., Jl. Ac. N. Sci. Phila. II, p. 296, PI. 
XXVI, Fig. 5; 1888—B. H. Wright, Check List. 
1900b—Quadrula hebetata Simpson, Proc. U. S. Nat. Mus., XXII, 
P. 787. 
ANIMAL CHARACTERS :—The soft parts of a form of F. hebetata, 
found in the Osage River, were discovered to be indentical with 
those of F. flava. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell rather orbiculate-quadrate, 
thick, moderately inflated, post-umbonal ridge prominent, disk 
smooth, beaks flat, and well back from the anterior end post- 
dorsal ridge rounded, post-ventral margin gently undulate; 
epidermis black with a few faint imbricated rays toward (but 
not across) the disk in the middle of the umbonal region. 
INTERNAL STRUCTURES:—Cardinals single in right, double 
