76 Natural History Bulletin. 



U. LiGAMEXTiNUs. — Lea. 



Extremely common and very variable. Nacre, white, pink 

 or purple. Rays green or brown, or wanting, when the shells 

 become uniform brown. Forms like U. upsotii, which is 

 clearly a synonym, are often found. 

 U. LUTEOLUS. — Lam. 



A common species. The form which sometimes occurs in 

 ponds has a thinner shell and is more distinctly rayed. Found 

 in streams or ponds in mud or sand. 



U. METANEVER. Raf. 



Common, sometimes with pink nacre. More compressed 

 forms are called U. wardi., but there is no excuse for the use 

 of this name. 

 U. MULTiPLicATUS. — Lea. 



Not common. Found in the Mississippi. 



U. MYTILOIDES. Raf. 



Reported from the Mississippi by Prof. Call and Prof. 

 Witter. 

 U. OBLiQUUS. — Lam. 



Reported from the Mississippi. 



U. ORBICULATUS. Hild. 



Not common. Found in the Mississippi, Cedar and Iowa 

 rivers. Some forms approach U. ellipsis very closely. This 

 is the same as U. higginsi. 

 U. PARVUS. — Barnes. 



Very common in the Iowa and Cedar rivers and their 

 tributaries. Found in mud and sand. Young specimens are 

 rayed. 

 U. PLiCATUs. — Le Seller. 



Very common, especially on muddy bottoms. Found in all 

 of our large streams. Old specimens are very obhque. The 

 adults are black, the young greenish yellow. 



U. PREssus. — Lea. 



Found in the Skunk and Shell Rock rivers. Rather rare. 



