118 THE NAUTILUS. 



Species: heterodon (Lea) — mar giJiata (Sa,y) [and var. varicosa 

 (Lam.)] — undulata (Say).' 



2. Genus: Strophitus Kaf.* 



Species: undtdatus (Say) [= edentulus (Say)]. 



3. Genus : Symphyt^ota Lea. 



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

 costata (Raf.) — comphinata (Barn.). 



4. Genus: Anodontoides Simps. 



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



5. Genus : Anodonta Brug. 



Species: cataracta Si\y. — ^ranrfts Say (witli several varieties) 

 imbecillis (Say.)* 

 4. Subfamily: Lampsilin^. 



Water tubes similar to those of the Unionin<x. 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. 

 Mursiipium 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 IJnionina, rarely different, and rectangular with two spines. 



1. Genus : Ptychobraachus Simps. * 

 Species : phaseolus (Hildr.) 



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

 closely related. 



*The marsupium oi Strophilus is very peculiar and complex, and cannot be 

 explained in a few words and without figures. Tbe discharge of the "pla- 

 centas" (''ovisacs" of Simpson) is 7iot 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 oi Anodonta, from Texas, which 

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

 A. henryana Lea (or may be a new species), 



*The peculiar character ot the marsupium of Ptychobranchus is well 

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

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

 should follow after Ptychobranchus. 



