<)2 THE NAIADES OF MISSOURI 



• not so pointed posteriorly, older shells tending toward post-dorsal 

 trunction, dorsal line arched, v^entral rather straight, epidermis 

 brownish; nacre white with pinkish umbonal cavity or solid color. 

 Sex Length Height Diameter Locality 



9 70 X 30 X 20mm (Black R., Williamsville) 



cf 56 X 26 X 13 " ( " " " ) 



9 46 X 23 X 12 " ( " " " ) 



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 suhgihhosus. 

 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. 



Elliptic dilatata delicata (vSimpson). 

 ("Little Lady Finger.") 

 PI. XXL, Figs. 68 A—D. 

 1900b — Unio gibbosus delicatus Simpson, Proc. U. S. Nat. Mus., XXII, 

 p. 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 



d" 55 X 26 X 13 " (White R., Holltster) 

 9 48 X 24 X 1 1 " ( " " " ) 



cf 43 X 21 X 10 " ( ) 



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. 



