68 



MOLLUSCA. 



POTAMIS. 



338, Cerithium rigidwn, Fleming, Brit. An. p. 358. Buc- 

 cinwm rigidwn, Brander, p. 43. 



Conical, general surface smooth; body not a tliird 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 hp 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 decorticafed. 



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 costs, 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 carinae, and 

 somewhat recurved. 



Found in the London Clay at Barton ClifT, and at Headon 

 Hill, Isle of Wight. 



Distinguished from P. Melanoides 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. de Paris, p. 

 84. Terehra 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 

 carinse near the margin of the base, which is somevthat 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 Headon Hill, and 

 also in the same formation. Isle of Wight. 



It may be distinguished from the P. Lamarcliii in its beak being 

 longer, and in the plait upon the columella. 



8. P. MARGABiTACEUs 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. 

 340, 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. XXXVIL 



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 lower ones with three ; 

 base of the body flat, with tv\o 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 be 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, lerminating in a 

 short, narrow, and slightly curved canal ; outer lip but little 

 bent, and inflected. 



