lip : the plait upon the columella is independant of the 
inner edge of the beak, which is obtuse. It differs from 
P. Lamarckii of Brochant in having a longer beak, and 
this plait upon the columella. 
From the same formation as the last ; collected by 
Mr. G. B. Sowerby at Headon Hill. 
POTAMIDES? plicatus. 
TAB. CCCXL. — Fig. 2. 
Spec. Char. Subulato-conical, or subcylindrieal ; whorls 
longitudinally plaited, transversely sulcated and 
striated ; sulci 3 or 4 ; base convex ; lip crenulated. 
Syn. Cerithium plicatum. Lamarck Env.de Paris, 84 . 
The crossing of the sulci over the plaits form arched 
rows of obtuse tubercles ; the plaits are deepest upon the 
upper part of each whorl, so that the base appears less 
regularly tuberculated ; the beak is rather contracted, 
and there is moreover a small canal at the upper angle 
of the other ways round aperture. 
Found in the upper marine formation, upon the Isle 
of Wight, by Prof. Sedgwick. 
POTAMIDES duplex. 
TAB. CCCXL. — Fig. 3. 
Spec. Char. Subulato-conical, with two rows of tuber- 
cles upon the upper, and three upon the lower whorls ; 
upper rows of tubercles largest ; sides of the whorls 
flat ; base flat, with two carinae near its edge ; beak 
short, inner edge rising upon the columella. 
Thi s differs from P. cinctus in having only two rows of 
granules upon the upper whorls, and in their being so 
