392 Quarterly Journal of Coiichology. 



male disk ellii^tical, female quadrate and more tumid. It 

 is probably orbiculaia, Heild. 

 U. L^EVissiMUS, Lea. Common; Mississij^^i and Cedar. Polished 

 flesh-colored epidermis, thin, purple inside, dorsal wing; 

 seems to prefer sandy bottom. 



U. LiGAMENTiNUS, Lamarck. Abundant; Mississippi, Cedar, Iowa, 

 and DesMoines. Variable in form and color, epidermis 

 strongly rayed with green, and inside bluish white, red rays 

 equally strong, and inside rose to purple. Shell heavy; 

 some forms difficult to separate from lufeolits, Lam. 



v. LUTEOLUS, Lamarck. Abundant in Cedar and DesMoines 

 but rare here. I have found it in the Mississippi and in 

 Muscatine Slough below Keokuk Lake. Extremely variable 

 in form and color; from long and slender beautifully green 

 rayed to tumid, truncated, yellow. Difference in form is 

 no doubt due in great part to sexes. It seems to vary to 

 ovatus. 



v. METENEVRUS, Rafiuesque. Abundant; Mississippi. A beautiful 

 shell, quite variable in form. 



U. MississiPPiENSis, Conrad. Abundant; Muscatine Slough. Light, 

 dark green to black, sexual difference well marked. Seems 

 to avoid running water. Closely related to nasutiis, Say. 



LT. occiDENS, Lea. Common; Mississippi. Very tumid, beautifully 

 green rayed, light salmon to pink inside; old shells much 

 eroded. Same form as capax. 



U. PARVUS, Barnes. Rare; Muscatine Slough, ponds generally; 

 associated with Aiiodoiiia ijiihccilis and Unio viiisissippieusis ; 

 length 3.7, width 2 cm. 



U. PLiCATUS, Barnes. Abundant; Mississippi. Very heavy; but 

 two or three well marked folds, folds sometimes almost 

 wanting; purple about posterior adductor scar and along 

 posterior margin; rather globular. 



