Umbones depressed; shell about 10.12 x 8 x 3.9 cm. 



Q. undulata (Barnes) Bak. 



Shell tubercled. 



With a strong posterior fold or ridge. 



Q. metanevra (Raf.) Simp. 

 Without strong fold, at most with low ridges. 



Posterior ridges two ; tubercles mostly in two rows. 



Q. lachrymosa (Lea) Bak. 

 Posterior ridge one or none; tubercles usually scattered, 

 many. Q. pustulosa (Lea) Bak. 



Shell smooth, without folds or tubercles, sometimes with pos- 

 terior ridge. 



Posterior ridge absent or indistinct. Q. coccinea (Con.) Bak. 

 Posterior ridge distinct. 



Umbones large; dimensions about 7.8 x 5.8 x 4.1 cm. 



Q. trigona (Lea) Bak. 

 Umbones less inflated, shell flatter; about 5.9 x 5.8 x 3.6 

 cm. Q. ruhiginosa (Lea) Bak. 



48. — Truncilla — one species in Iowa. 



49. — Flagiola — one species in Iowa. 



50. — Ohovaria ellipsis (Lea) Simp. 



51. — Tritogonia tuherculata (Barnes) Simp. 



52. — Fleurohema aesopus (Green) Simp. 



53. — Oiliquaria reflexa (Eaf.) Bak. 



54. — Cyprogenia — one species in Iowa. 



55. — Hemilastena — one species in Iowa. 



56. — Symphynota 



Shell suborbicular, very flat, winged; teeth obsolete. 



S. complanata (Barnes) Simp. 

 Shell elongated, more inflated, scarcely winged. 



Lateral teeth absent. S. costata (Raf.) Simp. 



Lateral teeth present. S. compressa Lea. 



57. — Margaritana — one species in Iowa. 



58. — Arcidens — one species in Iowa. 



59. — Alasmidonta truncata B. H. Wr. 



60. — Stropliitus edentulus (Say) Con, 



61. — Anodontoides 



Shell thin, not cylindrical. A. ferussacianus (Lea) Bak. 



Shell thicker, larger, subcylindrical. 



A. ferussacianus var. suhcylindraceus (Lea) Simp. 



62. — Anodonta 



Thin, inflated, with straight hinge line; umbones depressed. 



A. imhecillis Say 



Heavier, broader, umbones prominent. 



Beaks with 5 coarse wrinkles; greenish. A. grandis Say 



Beaks with 4 fine wrinkles; brownish. A. footiana Lea. 



88 



