262 THE AMERICAN MIDLAND NATURALIST 
the main body of rivers but in such cases there was always some 
slough, bayou, or lake near by from which its light shell may have 
been carried over in time of flood. This species has a general 
distribution over the Mississippi and St. Lawrence basins. In 
this state it is confined to the lake district of N. W. Missouri, 
and in the lacustrine conditions of Central and South West Mis- 
souri. Its breeding season seems to be continuous for the year, 
or at least there is a very short interim of sterility. The author 
examined it nearly every month of the year to find it gravid and 
that, for the most part, with mature (active) glochidia. The 
“eye spots,’ mentioned by Simpson, as characteristic marks on 
the mantle edge at the branchial opening, have not been observed 
by the writer. Because of its Anodonta-like marsupia, but more 
on account of its physiological characters, in being a hermaphrodite 
with an almost continuous breeding season, this species should be 
assigned to a little higher position in the genus than suborliculata. The 
fact that Rafinesque used ohiensis as the type for his genus Lastena 
and also because of such departure in anatomical and concholo- 
gical features from those of the genus Anodonta for ohiensis and 
its nearest ally, suborbiculata, this genus Lastena should now be 
employed for these two species of this State. 
Genus, Anodonta Lamarck. 
1799—Anodonta Lamarck, Prodrome Class. Coq., p. 87. 
1817—Anodontes Cuvier, Regne. An., II, p. 472. 
(Type, Mytilus cygneus Linnaeus). 
ANIMAL CHARACTERS:—Branchial opening with yellowish 
papillae, anal smooth to slightly crennulated; supra-anal generally 
small, removed from anal by long mantle connection; inner lamina 
of inner gills free from one-half to entire length; palpi usually long 
and large; only outer gills marsupial, when marsupia are gravid, 
ventral edge distends and secondary water-tubes appear, ovisacs 
simple, undivided, dark brown when gravid with mature glochidia; 
no conglutinates formed; glochidia large, brownish, spined, 
spadiform. 
SHELL CHARACTERS:—Shell elliptical, inflated, thin, slightly 
alated; disk smooth; beaks full high, sculpturing distinct, double- 
looped, angled upward centrally; epidermis polished, brightly 
colored; hinge teeth completely lacking. 
-No genus is so susceptible to so many mutations, yet it is 
