202 ’ THE AMERICAN MIDLAND NATURALIST 
The last two measurements are those of the most adolescent 
shells at hand but are not young enough to present much addi- 
tional information than can be obtained from the mature shell. 
MISCELLANEOUS REMARKS:—This is one of the species of very 
wide geographic distribution in United States but is limited in 
this state for the interior to those streams south of the Missouri 
River where it is met with in a multitude of forms—especially 
of the small thin and compressed varieties found in the Ozarkan 
streams of South Missouri. In the Osage it is found most typically, 
aside from the Mississippi which produces the best types of all 
Natad species. The depauperization of this species in size and form 
in the mountain streams is evidently due to a swifter current and 
hence these dwarfed forms may be merely a local ecologic race 
that may not deserve special names; however, two forms in this 
state occur often enough to require some little attention. 
Dilatata (Raf.) (=gibbosus (Bar.)) is more confused with Ellip- 
sara clintonensis (Simpson) than with any other shell. There is a 
difference, however, in the latter possessing capillary rays, and 
a broader interdentum, but the best distinction is in the marsupial 
structures of the latter that presents a folded appearance, when 
gravid. Simpson did not know the difference from shell structures 
until he found a gravid clintonensis. While this species is both 
lacustrine and fluviatile, yet it is never found in any lake or pond 
in this state. The typical dilatata with white nacre (E. arctior) is 
simply put down in the synonomy. A form like Conrad’s U. arcus 
is sometimes found in the Osage but aside from its shortened 
dwarfed form of shell it does not even possess enough differentia- 
ting characters to give it a varietal place. The writer has found 
it to be gravid only from June to August; hence tachytictic. 
Elliptio dilatata subgibbosa (Lea). 
(‘Little Lady Finger,’ ‘‘Little Spike.’’) 
Pl. XXI., Figs. 68 A—D 
1857—Unto subgibbosus Lea, Pr. Ac. N. Sci. Phila., IX, p.169; 1858, 
JleAc: N. Set;Phila., TV, "pt 53) pla, ne. or 
1868— Unio lazarus Sowerby, Conch, Icon., XVI, pl. LX VIII, fig. 348. 
ANIMAL CHARACTERS:—Absolutely identical with those of the 
parent. No real difference in glochidial characters even. 
SHELL CHARACTERS:—Moderately small, short, rather in- 
flated, somewhat heavy through the post-ridge, more elliptical, 
