400 THE AMERICAN MIDLAND NATURALIST 
ANIMAL CHARACTERS:—Siphonal openings well formed; 
inner laminae of inner gills usually entirely connected to the 
visceral mass; in male no specialization, but in female the inner 
edge of mantle antero-ventrad to branchial opening always with 
well developed papillae, or short tentacles which often extend to 
the central of ventral edge; marsupium reniform, swollen, con- 
sisting of many ovisacs occupying posterior part of outer gill 
and ventral edges beaded in white or black pigment when gravid; 
conglutinates white, not very solid; glochidia ‘large or medium 
in size, semi-elliptical. 
MISCELLANEOUS REMARKS:—The special structures on the 
mantle antero-ventrad to the branchial opening would group 
this genus among the highest of the Lampsilinae from the fact 
that the aération of the embryos is well secured through such 
specialization. Especially because of the number, form and 
arrangement of the papillae two sub-genera may be marked out. 
In the following description when the specialized mantle edge is 
discussed the female is considered. 
Sub-genus Micromya Agassiz. 
(Type, Unio fabalis Lea.) 
1852—Micromya Agassiz, Arch. fiir Nat., p. 57; 1912b, Ortmann, 
{Niel (CGe, IME SS WAU oR” Sie pe 
ANIMAL CHARACTERS:— Mantle edge antero-ventrad to bran- 
chial opening specialized by papillae, both regular and irregular, © 
arranged rather widely separated in a single row but never 
extending to the middle of the ventral margin; inner laminae of 
inner gills entirely connected, or more or less free. 
SHELL CHARACTERS :—Shell sub-elliptical, small or medium in 
size; beak sculpture rather double looped-or distinctly sinuate 
with the posterior sinuation rather open. 
MISCELLANEOUS REMARKS:—This sub-genus is represented 
in this state by three species—all found only in the Ozarks. 
The type fabalis of Lea of Micromya is not found anywhere in 
Missouri. The essentia] distinction between the two sub-genera, 
Micromya and Eurynia (sens. strict.) is in the less extensive and 
less crowded arrangement of the papillae on the inner edge of the 
mantle antero-ventrad to branchial opening in the former. 
(To be continued. ) 
