os) 
24 THE AMERICAN MIDLAND NATURALIST 
Genus Obovaria Rafinesque. 
1819—Obovaria Rafinesque, J. de Phys. Chim. Hist. Nat., p. 426. 
(Type, Unio retusa Lamarck.) 
ANIMAL CHARACTERS:—Branchial and anal opening both 
papillose; supra-anal large, crenulated; mantle margin antero- 
ventrad to branchial opening slightly specialized with lamellae 
or crenulations; inner gills twice the width of outer, inner laminae 
entirely connected to visceral mass; palpi small, far removed from 
anterior end of outer gills; color of soft parts soiled white; mar- 
supium consisting of many ovisacs originating from posterior 
half of outer gills and extending far below the ventral edge; con- 
glutinates poorly developed, embryos being held in rather loose 
masses; glochidia somewhat large, semielliptical, spineless, hinge 
line undulate. 
SHELL (CHARACTERS:—Shell rounded or ovate, inflated, 
height, greater than length; post-umbonal ridge not distinct, 
disk smooth; beaks prominent, sculptured with a few indistinct, 
concentric, sinuate bars; epidermis brown with faint rays. 
MISCELLANEOUS REMARKS:—Although this genus is another 
one of the primitive types of Lampsilinae, yet the differentiation 
of the mantle border antero-ventrad to the branchial opening and 
the tendency of the marsupium to assume the reniform shape 
and to acquire a position near the opening of the incoming currents 
all show and approach to the more modern groups. According 
to Dr. Ortmann the sub-genera of this genus, as fixed by Simpson, 
are well deflned enough to be retained. 
Thus we have the following grouping :— 
1.—Sub-Genus Obovaria (sens. strict.) 
Shell upright, oval, rather solid; beaks drawn up more 
toward the middle of the dorsal line; cardinals mostly normal. 
Type, O. retusa (Lamarck.) 
2.—Sub-Genus Pseudo6n Simpson (1900b, p. 601). 
Shell oblique, elliptical, solid, thick; beaks protruding 
anteriorly; cardinals subparalle] to laterals. 
Type, O. ellipsis (Lea) 
From the above diagnoses it may seem that division is made 
on the shell characters, the soft parts being identical,—even in 
marsupial and glochidial characters. However, this Genus is 
