48 
divided by two opposite ridges, so as to fit very close when 
the animal is distended, and prevent the introduction of 
foreign substances. A tube very similar is formed by 
the Teredo, and some Lithodomi deposit calcareous 
earth about the openings of their cells, apparently for 
the same purpose. The two valves of the shell are thin, 
obliquely elongated, with the beaks near the anterior 
extremity ; the oblique truncation of the anterior mar- 
gin leaves a large space between the edges of the valves 
for the passage of the foot : the posterior portion is 
large, oval, and its edges towards the back more or less 
gaping. 
We are indebted to the accurate observer Spengler, 
for the establishment of this very natural genus ; and if 
Bruguiere had never proposed the genus Fistulana, 
Conchologists would not have had to encounter the mass 
of confusion created by Lamarck, but have found good 
places for all the shells he has crowded into it, by the 
adoption only of Gastrochaena, in addition to the genera 
before formed. The genus Fistulana, as given by La- 
marck, has gradually been deprived of nearly all its 
species ; only one is retained by my brother, who has 
given an able account of this dismemberment. M. Des- 
hayes on the other hand, only deprives it of all the spe- 
cies that do not belong to Gastrochaena, which genus 
