106 THE AMERICAN MIDLAND NATURALIST 
Before maturity the glochidia have been observed to be yeliow- 
ish brown and contained in pinkish sacs. 
Fusconaia undata trigona (Lea). 
(‘Little Pigtoe.’’) 
Plo. “Ftgs..37 Ay and B: 
1913a—Fusconaia undata trigona (lea) Ortmann, Pr. Am. Phil. Soc., 
TT, wNoty. 200; 
ANIMAL CHARACTERS. 
The nutritive and reproductive structures of this subspecies 
are, of course, identical with those of its species. 
SHELL CHARACTERS. 
Shell more quadrate than that of fF. flava, post-umbonal 
ridge not so prominent, more solid anteriorly, higher fuller beaks, 
epidermis darker. Compared to its typical species it never matures 
to be as large, nor as heavy, is not quite so upright, nor as inflated, 
has lower beaks and more of a reddish epidermis. The internal 
shell structures are identical with those of its species. From the 
subspecies, trigonoides, it differs chiefly in being more upright, 
not so elongated, nor as large. 
Length Height Diameter Locality 
Gstaad (Osage, R., Sagrada, Mo.) 
6Oi x 50: x 32mm (ari? 74 Monegaw Springs, Mo.) 
60 7x 54 Xx 34mm Cus ” Warsaw, Mo.) 
48.5 X 40 x 26mm (s4afe ” Tjinn Creek, Mo.) 
MISCELLANEOUS REMARKS:—This sub-species is one of the 
decided intergrades for F. undata and flava and is the most common 
form in the interior streams of the state—especially in the Osage 
where the writer, in a 300 mile survey by boat, made a thorough 
study of them to find the interior of shell and soft parts to be 
identical with those of the species; however, none of these forms 
were found with reddish conglutinates, nor yellowish soft parts. 
Probably this whitish colorization was due to the advanced stage 
of gravidity in which they happened to be found when they were 
encountered between the upper and lower stretches of the river. 
at the latter part of July. This variety of wndata may be ecolo- 
gically determined as a dweller in medium sized rivers, or, if found 
in a large river, in medium stream conditions. This is found to 
be the case in the Osage, for the more the mouth is approached 
the more this form is supplanted by the heavier, more inflated 
