266* 



he denies its being a sea shell, and finds it necessary to 

 consider it as belonging to the marshes adjoining the sea, 

 or to the salt water of the mouths of rivers : and finding 

 other species as having been said to be found in these 

 situations, he thinks it necessary to form a genus for their 

 reception, founded rather upon the habits of the animal 

 than on the characters of its shell. Thus we are led to the 

 consideration of supplementary genera. Cerithia was 

 supposed by M. Brongniart to be actually divisable into sea 

 and into fresh-water shells. To the former he continued 

 their original designation cerithium : the latter he named 

 potamides, and distinguished as " a turriculated shell ; 

 opening nearly semicircular, pinched up as it were at the 

 base of the columella, and terminated by a very short, 

 straight, canal, which is hardly grooved ; there being no 

 groove at the upper extremity of the right side." 



Turbo is generally a sea shell, though sometimes found 

 in ponds of salt water. The sea and river patella, it is 

 acknowledged, differ hardly at all in their shells, but must 

 thus be placed in different genera : and the same must be 

 remarked of the crepidula, he, I believe, meaning calyptrea. 

 Ctjdostoma must be divided into cyclostoma for the land 

 shells, and puludina for the aquatic shells. Marine bulimi 

 must be separated from the land bulimi, and be disposed 

 in a new genus, or joined to phasianella. Melania, auricula, 

 cimpullaria, planorbis, and nerita, all demand subdivision. 

 Pupa, also, he says, requires subdivision ; but, as in the case 

 of patella, the shells would be difficultly distinguishable. 



Of the particular shell mentioned by M. Brard, he 

 makes a species of this genus, and terms it Potamides 

 Lamarckii.* By thus dividing genera into those of sea, 



* This conciliatory compliment to M. Lamarck appears to have 

 been by no means unnecessary. For those who attempt to explain 

 the circumstance of the mixture of sea, river and land shells, bv 



