48 
might with less hesitation point out which of those at 
present called Cerites ought to be removed to Potamides, 
but the two genera are as likely to be mixed as the 
Oysters, Cyclades, Malanopses, Ancillas, &c. that ac- 
company them, in beds, between the two fresh water 
strata, on the Isle of Wight, or above the white Sand 
at Charlton, &c. 
If the characters above mentioned could be relied 
upon, which we fear is not strictly the case as far as 
concerns the form of the mouth, the following species, 
published at tab. 147, should be arranged as Potamides, 
Cer. funiculatum, Cer. intermedium, Cer. dubium, and 
Cer. M elan io ides ; the two last have the best claim to 
removal ; perhaps Cer. funatum, tab. 127, ought also to 
be removed ; it appears to have a small groove or canal 
at the junction of the right lip with the spire, although 
hardly enough to be considered of importance ; indeed 
such a groove is observable in some of the recent Po- 
tamides. 
POTAMIDES rigidus. 
TAB. CCCXXXVIIL 
Spec. Char. Subulate-conical, nearly smooth; 
lower whorls surrounded by a keel near 
their upper parts. 
Syn. Buccinum rigid um. Hr cinder, 43. 
Some obscure furrows indicating the lines of growth are 
observable regularly covering the otherways smooth sur- 
face of this shell : from the Cyurvature of these lines, and 
