Ortmann: Families \m> Genera oi Najades. 239 



knew 11 in European forms, where thej incline toward the type <>t the 

 subfamily Anodontince. I have no doubl that this finally will be a 

 verj important systematic criterion, but unfortunately we do not 

 know the glochidia of a nn^le Asiatic species. 



The following provisional division into genera in accordance with 

 what has been hereinbefore said is here submitted: 



Beak-sculpture ranging from the concentric to 1 1 1 « - zig-zag type. Mantle con- 

 nection between anal and supra-anal absent, deciduous, short, or of 

 medium length. Inner lamina of inner gills free from abdominal sac. 



6l. Mantle connection absent or short. Beak -sculptllie coiieentii< 1,, iv 



Glochidia subovate, without hooks. 

 ci. All four gills serving as marsupia. Mantle connection between anal 

 and supra-anal present, short and deciduous. 9 

 di. Ovisacs and placentae 10 subcylindrical, the latter rather persistent, 

 generally red. Shell simple, without sculpture upon disk. Beak- 

 sculpture simple, concentric Fusconaja. 



d z . Ovisacs and placentae leaf-shaped (compressed and lanceolate), the 

 latter rather poorly developed, generally white. Shell with 

 sculpture of various patterns. Beak-sculpture concentric, 

 double-looped, or zig-zag. 

 Shell with oblique undulation- upon the disk. Beak-sculpture 

 concentric, nearly obliterated, or of zig-zag pattern and 



extending more or less upon the disk Crenodonta. 



ft. Shell-sculpture tuberculous or nodulose. Beak-sculpture con- 

 centric and disappearing upon the disk, or of the double- 

 looped or zig-zag pattern, more or less extending upon the disk. 



Quadrula. 

 cs. Marsupium formed by the outer gills only. 



d\. Mantle-connection above anal opening absent, no supra-anal formed. 

 Shell tuberculous, beak-sculpture of zig-zag pattern, much 

 broken up, extending somewhat upon the disk. Xacre deep 



purple Rotundaria. 



dt. Mantle connection between anal and supra-anal present, short, or 

 deciduous. Beak-sculpture concentric, obliterated toward 

 the disc. 

 ft. Shell tuberculous. Soft parts of a peculiar orange color. Pla- 

 centa.- pink (at least in one species) Plethobasus. 



• Under this division apparently belong two species occurring in Georgia and 

 Florida, infucata Conrad and kleiniana Lea, the soft parts of which have been partly 

 described by Lea (Obs., X, 1863, pp. 404 and 407). In these species we observe the 

 most beautifully developed zig-zag sculpture among Xorth American forms. The 

 soft parts are imperfectly known, but the marsupium is formed by all lour gills. 

 Probably they should form a genus by themselves. 



10 Called "egg plates" by Lillie (1895), and " conglutinates " by Lefevre and Curtis 

 (1910). 



