252 



Unio nigrinus. 



„ nux. 



,, Oregonensis. 



„ perstriatus. 



„ placitus. 



„ Powellii. 



„ Prevostianus. 



5, proximus. 



„ pygmaeus. 



„ Reevesianus. 



Anodonta Arkansensis. 

 „ Californiensis. 

 „ denigrata. 

 „ Linnseana. 

 „ oblita. 

 5, opaca. 



Unio rufusculus. 

 Rumphianus. 

 sagittaformis. 

 satur. 

 sordidus. 

 Stewardsonii. 

 succissLis. 

 Troschelianus. 

 Tuomeyi. 

 Whiteianus. 



Anodonta Schroteriana. 

 ,, ShaefFeriana. 

 ,, tortilis. 

 „ Troutwiniana. 

 „ virens. 

 „ Wheatleyi. 



2. — " Description of a New Genus (Basistoma) of the Family Me- 

 laniana, together with some New Species of American Mela- 

 nice.'''' — By Isaac Lea. 



In this paper the genus Basistoma is thus characterised : 



B. Testa conica. Apertura ovata, basi abscissa. Labrum acu- 



tum. Columella Isevi. Operculum . 



There are described in this paper one species of Basistoma, and 



eleven of Melania, viz : 



Basistoma Edwardsii. 

 Melania Brumby i. 



„ Clarkii. 



5, furva. 



„ gibbosa. 



„ oblita. 



Melania oppugnata. 

 „ pinguis. 

 5, perstriata. 

 „ Sellersiana. 

 „ sculptilis. 

 „ Saffbrdii. 



3. — Description of a New Species of Helix, from California, 

 and a new characteristic form of certain American Colima- 

 cea." — By Isaac Lea. 



In this paper the diagnosis of the Helix Lecontii is given, and the 

 accessory column described, which the author had observed in cer- 

 tain species, and to which he has supplied the name of Fulcrum, being 

 a kind of buttress. He described it as being placed, or soldered, as it 



