320 THE AMERICAN MIDLAND NATURALIST 
ventrad in male, slightly swollen in female; whole shell medium 
in size, small but more inflated; disk from beaks to central-ventral 
edge sculptured with a row of a few large knobbed tubercles, 
those of one valve alternating with the knobs of the other; post- 
umbonal ridge with corrugations; epidermis yellowish-green to 
dark brown. 
INTERNAL STRUCTURES:—Cardinals upright, jagged; laterals 
short, nearly straight at right angles to a rather broad interdentum 
beak and branchial cavities moderately deep; nacre a pure, 
stippled white. . 
Sex Length Height Diameter Locality 
SO De See oe ep onban (Platte R., Platte R. Station) 
9 55 x 45 %* 30mm+——(Marais des Cygnes, Athol) 
oS 35 xX 26 x 17mm——(Platte R., Dixon Falls) 
9 20 x 15 x 12mm——(Miss. R., Hannibal) 
Ki e2O xe 7 DAS) 9.5mm——(Crows Fork, Fulton) 
The last two are measurements of juveniles of widely different 
locality under far different ecological conditions, although the 
shell characters are not very much different. The former shows 
more of a rayed olivaceous epidermis and the latter a plain straw 
color. The Mississippi juvenile, being more typical as in case of 
most shells, is described here:—Shell sub-trigonal, valves inequi- 
lateral with two knobs on one side and one on the other, darker 
green epidermis below the knobs, rayed with interrupted V- 
markings, beak sculpture irregular concentric undulations extend- 
ing out on disk; nacre white, slightly tinged with pink. 
MiIscELLANEOUS REMARKS :—Both as to structure of shell and 
nutritive soft parts O. reflexa is rather primitive, but as to marsupial 
characters it naturally falls under the lower groups of the Lampsi- 
linae. In North Missouri reflexa reaches a very large growth while 
in Central Missouri it averages only about one-half the size; for 
the two faunae this variation applies to many other species. Since 
Drs. Lefevre and Curtis (1912, pp. 137 and 138) have called 
attention to the eccentric breeding habits and glochidial behavior 
of reflexa the writer has followed up the breeding period rather 
closely to find that it is gravid with early and late embryos, also 
with glochidia, during June, July and August, but is sterile for 
late Fall and mid-Winter, thus showing that this species has a 
short period of gravidity,—a different reproductive habit from 
