ae 
— toe 
THE NAIADES OF MISSOURI 203 
not so pointed posteriorly, older shells tending toward post-dorsal 
trunction, dorsal line arched, ventral rather straight, epidermis 
brownish; nacre white with pinkish umbonal cavity or solid color. 
Sex Length Height Diameter Locality 
Oar 70) xa) 20 px. 2omm (Black R., Williamsville) 
CPPS Gye 20) ED BB e277 hy, (ee i w ) 
Co} PurOTlL Gis io ¢ Suapee de Wore eae on 72 ea Gisiert, 4 a ) 
MISCELLANEOUS REMARKS :—Specimens collected from streams 
in Stone County have been sent to the Division of Mollusks in 
the National Museum where they were identified as subgibbosus. 
It has also been reported from the streams of Texas and Shannon 
Counties. It is different from the variety delicatus of Simpson 
by being somewhat larger, not so thin-shelled, more arched dorsad, 
more pointed both anteriorly and posteriorly, with rather promi- 
nent post-umbonal ridge. This variety is rather common in the 
Black and St. Francis drainage. 
Elliptio dilatata delicata (Simpson). 
(“Little Lady Finger.’’) 
PISGAH TOS, OO) ga —— 
1900b— Unio gibbosus delicatus Simpson, Proc. U. S. Nat. Mus., XXII, 
Pp. 704. 
ANIMAL CHARACTERS :—Although the anatomy of this variety 
is smaller than the parent, yet it is precisely identical. Only sterile 
individuals found; however, only outer gills marsupial. 
SHELL CHARACTERS:—Shell greatly compressed, very small, 
thin, outline evenly elliptical; epidermis brownish red to oliva- 
ceous; hinge teeth rather prominent, thin, nacre purple or coppery- 
rarely white. 
Sex Length Height Diameter Locality 
(SH AG ip Seth Ooo Vai OS (White R., Hollister) 
OMA AS Me Rea ARM re Xo Male ios (Gnas Ma 41 ) 
Cul ARs Xoo Ty eX On (Shese ey " ) 
MISCELLANEOUS REMARKS:—The writer has in his collection 
a shell of this subspecies bearing the original label of Mr. Simpson, 
the author. The dilatata shells of the White River compare well to 
it. For the same ecologic reason we may account for this small 
form in the South Missouri drainage as well as for the occurrence 
of subgibbosa. These two forms are not found north of the Ozark 
divide, neither is the typical dilatata of Rafinesque found south of 
it in this State showing the ready response of the parent species 
to different environmental conditions, 
