THE AMERICAN MIDLAND NATURALIST 49 
32. S.complanata (Barnes)—(t1.a) 
33. S. costata (Raf.)—(3. c) 
Genus XII. ARrcIDENS Simpson) 
34. A. confragosus (Say)—(2. c) 
*(b)—Mantle connection between anal and supra-anal openings very 
long; hinge completely absent; disk smooth; shell thin. 
Genus XII. Lastena (Raf.) 
35. L. suborbiculata (Say)—(1. b) 
36. L. ohiensis (Raf.)—(1. b) 
Genus XIV. ANopontTa (Lamarck) 
37. A grandis (Say)—(1. b) 
38. A. dakotana Frierson —(tr. b) 
39. A. corpulenta Cooper—(t. b) 
40. A. Danielsii Lea—(1. a) 
41. A. Bealit Lea—(1. 2c) 
(c)—Mantle connection between anal and supra-anal openings 
moderately long; hinge almost absent; shell rather thin, disk 
tNSeUpltured ss. sue ss ae Genus XV. ANODONTOIDES (Simpson) 
42. A. ferussacianus (Lea)—(1. b—) 
b.—Inner laminae of inner gills with tendency to connect with vis- 
ceral mass; mantle connection between anal and supra-anal openings 
moderate; beak sculpture, heavy, concéntric. 
(a)—Marsupium with simple ovisacs; hinge teeth rather well de- 
veloped with cardinals sharp and prominent. 
Genus XVI. ALASmIDOoNTA (Say) 
43. A.calceolus (Lea)—(3. c) 
44. A. marginata Say—(2. c) 
(b)—Marsupium with transverse ovisacs; hinge rudimentary with 
cardinals rounded and suppressed. .Genus VXII. SrropnHitus (Raf) 
45. S. edentulus (Say)—(2. a) 
(C)—Mantle connection between branchial and anal openings present, 
never very long; inner laminae of inner gills rarely ever entirely free 
from visceral mass; post-ventral margin of mantle usually highly 
differentiated with papillae, flaps, etc.; part of outer gills in most 
genera specialized as marsupia, which, when gravid, bulging beyond 
original edge of gills, ruptured at ventral edge of ovisacs for escape of 
larvae; glochidia semi-circular, (I,AMPSILIS type), or axe-head shape 
(PROPTERA type), ventral margin rounded, rarely spined; bradytictic. 
Sub-Family III. Lampsininagk Ortmann. 
a.—Marsupium with subcylindrical ovisacs; post ventral margin of 
mantle smooth; shell sometimes with disk sculptured, sex dimor- 
phism of shell not distinct. 
(a)—Marsupium occupying almost entire outer gill, edges folded, 
ovisacs several, small, short....Genus XVIII. Eviipsaria (Raf.) 
46. EE. clintonensis (Simpson)—(3. c) 
(b)—Marsupium occupying outer gill in a few, large, long ovisacs. 
Genus XIX. OBLIQUARIA (Raf.) 
47. O. reflexa (Raf.)—(1. c) 
