POTAMIDi iS coneavus f » 
TAB. CCCXXX1X. — Figs. 1 and 2. 
Spec. Char. Subulato-conical, transversely striated ; 
volutions i rather concave towards the upper part, 
costated ; costse obscure, arched, with a slight emi- 
nence above the middle of each ; base with one or 
two granulated carinae, convex ; lip enlarged below, 
with a small groove in its upper angle. 
I he concavity near the upper edges of the volutions 
crossed by the irregular costas is the distinguishing mark 
of this shell : the columella is smooth with a produced 
and somewhat recurved base ; the aperture is nearly 
round, notched at the base, which forms a short beak ; 
the transverse striae are not very deep, so that in worn 
individuals they are wanting. 
I first received this from the Rev. Mr. Iremonger, 
who collected it on Barton Cliff, see fig- 1 ; it has since 
been met with in what is called the upper marine forma- 
tion at Ileadon Hill on the Isle of Wight, by my son 
G. B. Sowerby ; a specimen brought by him is given at 
fig. 2. This species differs from small worn specimens 
of P. Melanioides, with which it might easily be con- 
founded, in the length and curvature of its beak, as well 
as the concave surface of its whorls. Fig. 3 represents a 
small variety of P. Melanioides from Plumstead Heath 
for comparison. 
