118 THE NAUTILUS. 



Species: heterodon (Lea) — marginata (^Sa.y) [and var. varicosa 

 (Lam.)] — undulata (Say),' 



2. Genus: Strophitas 'R-aL^ 



Species: undidatus (Say) [^^ edentulus (Say)]. 



3. Genus : Symphynota Lea. 



Species: compressa (Lea) — viridis (Conr.).* 

 costata (Rat.) — complanata (Barn.). 



4. Genus: Anodontoides Simps. 



Species : ferussacianus (Lea) (and var. subcylindraceus (Lea). 



5. Genus : Anodonta Brug. 



Species : cataracta Say. — grandis Say (with several varieties) 

 imbecitlis (Say.)* 

 4. Subfamily: Lampsilin^. 



"Water tubes similar totboseof the Unionina. Supra-anal opening 

 separated from the anal, rarely entirely closed. Diaphragm normal. 

 Inner lamina of inner gills rarely more or less free from abdominal 

 sac, generally entirely connected with it. Mantle edge in front of 

 branchial opening crenulated, papillose, or with a peculiar flap. 

 Marsupium formed by the outer gill, or {mostly) by the posterior part 

 of the outer gill (sometimes only a section of the latter is used for 

 the marsupium). Edge of marsupium, when charged, rounded^ 

 distended and bulging out beyond the ends of the branchial filaments. 

 Water tubes in the gravid female simple. Glochidia generally of the 

 type of the Unionina, rarely diflFerent, and rectangular with two spines. 



1. Genus : Ptychobranchus Simps. * 

 Species : phaseolus (Hildr.) 



^ Alasmid. heterodon stands by itself, while marginata and undulata are more 

 closely related. 



*The marsupium of Strophitiis is very peculiar and complex, and cannot be 

 explained in a few words and without figures. The discbarge of the "pla- 

 centae" ("ovisacs" of Simpson) is not through the walls of the gills, as Simp- 

 son indicates (1. c, p. 616). 



^Symphynota compressa and viridis are hermaphrodites ! 



* As already Sterki has shown, Anodonta imbecillis is a hermaphrodite^ which 

 I am able to confirm. I know another species of Anodonta, from Texas, which 

 is also hermaphroditic ; it groups with imbecillis, and belongs possibly under 

 A. henry ana Lea (or may be a new species). 



*The peculiar character ot the marsupium of Flychobranchus is well 

 known ; this form reveals what is essential in the Lampsilis-type of marsupium. 

 The genus Cyprogenia Ag., which I had no chance to investigate, very likely 

 should follow after Ptychobranchus. 



