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138 THE NAIADES OF MISSOURI 



Sex Length Height Diameter Locality 



9 80 X 61 X 47 (Grand River, Sumner) 



cf^ 70 X 55 X 39 (Mississippi River, Hannibal) 



9 65 X 52 X 41 (Osage River, Warsaw) 



cf 30 X 24 X 18 (Mississippi River, Hannibal) 



9 2': X 20 X 14 ( " " " ) 



Beaks of these specimens of the last two measurements very 

 full, rounded, poorly sculptured although not eroded; more 

 inflated (comparatively) than adult shell; epidermis olive with 

 profuse paintings of green rays so as to giv^e the appearance of 

 olive green; post-ventral edge of shell more obliquely rounded 

 than in adult; nacre pearl blue. 



Miscellaneous Remarks: — From shell characters there is 

 no real sex dimorphism except a little greater inflation in the 

 female, but not only a less crowded arrangement of septa is seen 

 in gills of the male but there is a more intense black pigmentation 

 in the region of the branchial opening. The crenulated supra-anal 

 opening is surely a unique character and may indicate a conversion 

 oj this opening into the anal. The bare connection between the two 

 openings wou'd also indicate this merging. Although of rare 

 occurrence ellipsis reaches its greatest perfection for the interior 

 in the Grand River of North Missouri. It is found occasionally 

 in the Osage Basin, but never develops a shell as large, heavy 

 or bright as found in the Grand or in the Mississippi. This fact 

 of difference in size, color and solidity for the shells of these different 

 mussel faunae applies to most other species as well. Scammon 

 (1906, p. 306) reports this species as very active with strong 

 musculature and that he has traced this species for fifty yards 

 by its furrow in the Kansas River. This species is bradytictic. 



Genus Nephronaias Crosse and Fischer. 



1893 — Nephronaias Crosse and Fischer, Miss. Sci., Pt. 7, IL P- 556; 

 1900b, Simpson, Proc. U. S. Nat. Mus., XXH, p. 591. 



(Type, Unio plicatulus Charpentier.) 



Animal Characters: — Identical with those of Obovaria — 

 even in glochidial characters. 



Shell Characters: — ^Shell rounded to sub-elliptic and 

 elongate, usually compressed; posterior ridge rather indistinct, 

 beaks not near the anterior end, sculpture poorly developed, — 

 consists of a few faint double-looped bars; epidermis greenish 



