TO GEOLOGY. 99 
of the columella, where it is disposed to put on an obscure 
fold, is thicker. 
Eight species have been observed in England. One in 
the Coral Rag, five in the London Clay, and two in the 
Crag. M. Deshayes gives twenty-three in his Tertiary 
Tables—fourteen are from the Paris basin. 
In the Green Sand Formation of Jersey, Dr Morton 
thinks he has observed casts of the Bulla. In the Tertiary 
of Maryland, Mr Conrad has obtained one species, Bulla 
acuminata (Sowerby). 
FAMILY MELANIANA. 
GENUS PASITHEA.  (nobis.) 
Description. Shell turrited, sometimes umbilicate ; 
mouth entire, angular above, somewhat effuse at base ; 
columella smooth, thickened. 
Observations. The mouth of the shells in the genus pro- 
posed above has a strong resemblance to the genus Mela- 
nia.* It is, however, less effuse at the base, straighter and 
. 
* The distinguished geologist, M. Brogniart, in his ‘‘ Terrains du Vi 
centin,”’ page 58, describes three species of Melania, two of which might 
with propriety be placed in the genus Pasithea. He makes the following 
