124 THE NAIADES OE MISSOURI 



connected to anal, mantle edge here blocked in black at regular 

 intervals; inner gills much wider and longer than outer, inner 

 laminae connected about one-half way; palpi united almost to 

 their tips antero-dorsad; color of foot, palpi and adductors orange, 

 variable with age. 



Reproductive vStructurES: — Marsupia occupying outer gills 

 with secondary water tubes, ventral edges distended when gravid, 

 ovisacs occupied by several other smaller sacs arranged crosswise 

 facing the outer and inner laminae in which small, solid white 

 cords (placentulae) , containing the ova or two to ten larvae, are 

 situated; glochidia large, spined, spadiform, hinge line straight, 

 length greater than height, (0.35x0.285 min). 



SHELL CHARACTERS. 



External Structures: — Elongate-ovate, moderately solid, 

 inflated, post-umbonal ridge usually rounded; female shell more 

 obtusely (or biangulated) posteriorly than male; umbones rather 

 full sculptured by two or three very coarse, wavy concentric 

 ridges abruptly bent up behind; disk not sculptured; epidermis 

 usually a glossy brown, sometimes marked by bright green rays, 

 especially in young shells. 



Internal Structures: — Cardinals almost obliterated, more 

 pronounced in left valve, where it is rounded and placed just 

 under the beaks; laterals and interdentum lacking; umbonal 

 cavities deeper in female shell; nacre variable from solid salmon 

 or white, to cream or pearl-blue color. 



Sex Length Width Diameter Um. ra. Locality 

 9 95 X 55 X 38 — mm — 0.360 — (Marais des Cygnes R., 



Rich Hill, Mo.,) 

 27 — mm — 0.430 (Osage R., Linn Cr.,) 

 14 — mm — 0.330 (102 R., Wyeth, Mo.,) 

 13.5 — mm — 0.335 (Grand R., Darlington.) 



The last two measurements are those oj the only shells oj eden- 

 tuhis jound in the interior north oj the Missouri River and these are 

 juveniles. Unlike most adolescent shells of this species, both shells 

 are uni-colored except for a single brownish band parallel with 

 the growth lines near the ventral margin on a back-ground of 

 yellowish-green; hinge teeth and beak sculpture typically stro- 

 phitus; nacre of both about the same ; shell thin and transluscent. 



Miscellaneous Remarks: — 5. edentulus is rather easily 

 recognized even through casual observation by its somewhat 



