136 THE NAIADES OF MISSOURI 



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 defined enough to be retained. 



Thus we have the following grouping: — 

 I. — Sub-Genus Obovaria {seyis. strict.) 



Shell upright, oval, rather solid; beaks drawn up more 

 toward the middle of the dorsal line; cardinals mostly tiormal. 

 Type, 0. retusa (Lamarck.) 

 2. — Sub-Genus Pseudoon Simpson (1900b, p. 601). 



Shell oblique, elliptical, solid, thick; beaks protruding 

 anteriorly; cardinals subparallel to laterals. 

 Type, 0. 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 i;- 



