68 
MOLLUSCA. 
POTAMIS. 
338. Cerithium rigidum , Fleming, Brit. An. p. 358. Suc- 
cinum rigidum , Brander, p. 43. 
Conical, general surface smooth; body not a third the length 
of the shell; spire consisting of seven or eight gradually taper¬ 
ing, flattened volutions, separated by a very narrow and shallow 
suture, with a large, somewhat blunted carina towards their 
upper margin, or about one-third below the suture; the whole 
surface with many regular, curved grooves, or lines of growth ; 
aperture oval, ending in an extremely short, almost straight, 
very narrow canal, which may be regarded as a mere sinus; 
outer lip greatly expanded, and even on the margin; above the 
carina, the grooves are sometimes decussated. 
This shell differs much in the young and adult conditions; in the 
former it is nearly quite smooth, and terminates in an acute point, 
while in the adult the apex is generally decorticated. 
Found in the London Clay at Barton Cliff, Hampshire. 
6 . P. concavus —The Concave Potamis, pi. XXXVII. 
fig. 34. 
Potamides concavus. Sowerby, Min. Conch. IV. p. 50, pi. 
339> fig* 1> 2. Cerithium concavum , Fleming, Brit. An. p. 
358. 
Shell subulately conical, with transverse, shallow' striae; body 
nearly equal to the spire in length; spire consisting of nine 
or ten slightly raised volutions, separated by a shallow suture, 
and are a little concave towards their superior portion, with 
longitudinal, obscure, arcuated, irregular cost®, and a slight 
eminence above the middle of each; aperture nearly circular, 
notched at the base, terminating in a short canal, and hav¬ 
ing a slight groove in the upper angle; outer lip somewhat 
enlarged below, and a little inflected; columella smooth ; base 
convex, provided with one or two granulated carin®, and 
somewhat recurved. 
Found in the London Clay at Barton Cliff, and at Headon 
Hill, Isle of Wight. 
Distinguished from P. Melanoidcs by the concavity on the volu¬ 
tions and the curvature of the beak. 
7. P. cinctus. —The Girdled Potamis, pi. XXXVII. fig. 
26 . 
Potamides cinctus. Sowerby, Min. Conch. IV. p. 51, pi. 
340, fig. 1. Cerithium. cinctum , Lamarck, Env. do Paris, p. 
84. Terebra cinctus, Fleming, Brit. An. p. 347. 
Shell subulato-conical; body short; spire very long, taper¬ 
ing, consisting of ten or eleven somewhat inflated, and well 
defined volutions, terminating in an obtuse apex, each volution 
furnished with three belts of nearly equal granules, and two 
carin® near the margin of the base, which is somewhat flatten¬ 
ed; aperture subrotund, terminating in a longish canal, obtuse 
at its termination; columella provided with a single plait; outer 
lip pretty long, and thin. 
Found in the Upper Marine formation at Ileadon Hill, and 
also in the same formation, Isle of Wight. 
It may be distinguished from the P. Lamarckii in its beak being 
longer, and in the plait upon the columella. 
8 . P. margaritaceus —The Pearly Potamis, pi. XXXVII. 
fig. 33. 
Potamides margaritaceus. Sowerby, Min. Conch. IV. p. 
51, pi. 339, fig- 4. Murex margaritaceus , Brocci, p. 447, pi. 
9, fig. 4. Cerithium margaritaceum , Fleming, Brit. An. p. 
358. 
Conical, turreted ; body short, equal to a third of the length 
of the shell; spire long, consisting of ten or eleven moderately 
ventricose volutions, well defined by the suture, each furnished 
with five spiral bands of elevated bead-like tubercles, the first 
and fourth bands being minute, and the fifth larger than the 
remaining two, placed near the upper edge of the volutions, 
producing a subcoronated aspect; these numerous granules 
giving the surface a rough appearance; aperture subovate, 
oblique, narrowed to a point above, and terminating below in 
a rounded, short, slightly oblique canal; outer lip expanded, 
slightly inflected and plicated, with two or three furrows within, 
on its superior part; inner lip smooth, and broadly reflected 
over the columella, which is recurved and obtusely carinated. 
Found in the Upper Marine formation, Isle of Wight. 
9. P. plicatus. —The Wrinkled Potamis, pi. XXXVII. 
fig. 24. 
Potamides plicatus . Sowerby, Min. Conch. IV. p. 52, pi. 
310, fig. 2. Cerithium plicatum , Lamarck, Env. de Paris, p. 
84. Fleming, Brit. An. p. 358. 
Shell subulate, conical, or subcylindrical; body large, ventri¬ 
cose, not a third of its length; spire consisting of ten or eleven 
rounded and rapidly diminishing volutions, provided with longi¬ 
tudinal plaits, and three or four spiral sulci; these crossing the 
plaits produce arcuated rows of obtuse tubercles, the plaits 
being deepest on the superior portion of each volution, gives 
the convex base the appearance of being less regularly tuber- 
culate; aperture subovate, a little oblique, somewhat contracted 
above into a canal, and terminating below in a rather wide, 
slightly twisted canal; outer lip crenulated; pillar lip smooth, 
and rather broadly reflected on the columella. 
Found in the Upper Marine formation, Isle of Wight. 
10. P. duplex. — The Doubled Potamis, pi. XXXVII. 
fig- 19- 
Potamides duplex. Sowerby, Min. Conch. IV. p. 52. pi. 
340, fig. 3. Cerithium duplex , Fleming, Brit. An. p. 358. 
Shell subulate, conical; body short, not a third of its entire 
length; spire consisting of eleven or twelve rather flat and gra¬ 
dually' tapering volutions, separated by a narrow, ill defined 
suture, the upper ones being the largest and ornamented with 
two spiral belts of tubercles, and the low r er ones with three; 
base of the body flat, with two carinated ridges near its margin; 
aperture small, nearly round, terminating in a slightly twisted 
and oblique, short canal, with the inner ridge rising upon the 
columalla; outer lip a little waved. 
This shell is nearly allied to P. cinctus , but may be distinguished 
from it by having only two rows of tubercles upon the upper volu¬ 
tions, and also in their being so arranged as to give the spire the 
appearance of being nine-sided. The suture line is so indistinct, 
that the separations of the volutions can only he determined by the 
larger girdle of tubercles near their upper edge. 
Found in the Upper Marine formation, Isle of Wight. 
11. P. acutus. —The Acute Potamis, pi. XXXVII. fig. 
27. 
Potamides acutus. Sowerby, Min. Conch. IV. p. 53, pi. 
341, fig. 2. Potamidum acutum , Fleming, Brit. An. p. 358. 
Shell conical, turreted; body nearly equal to half its length; 
spire consisting of seven or eight inflated and deeply defined, 
acutely bicarinated volutions, terminating in a sharp apex; base 
convex, bistriated; aperture nearly orbicular, terminating in a 
short, narrow, and slightly curved canal; outer lip but little 
bent, and inflected. 
