POTAMIS. 



MOLLUSCA. 



67 



In some specimens the tubercles on the superior portion of the 

 volutions have a coronated appearance. 



Found in the Bkie Clay, or Plastic Clay, above the indurated 

 Marie, Castle-hill, near Ncwhaven, Sussex, and at Ilordwell 

 Cliff. 



5. C. PVRAMiDAi.is The Pyramidal Cerithium, pi. 



XXXVII. fig. 28, 2[). 



Cerithium pi/raniidalis. Sowerby, Min. Conch. II. p. Gl, 

 pi. 127, fig. 1, 1. Cerithium hexagonurn, Lamarck, Env. dc 

 Paris, p. 79. Murex he.ragonus, Chemnitz Conch. X. p. 2Gl, 

 pi. 162, fig. 1534-5. Murex angolosus, Brander, p. 24, fig. 4G. 

 Fleming, Brit. An. p. 397. 



Pyramidal, turreted ; body occupying about a third of the 

 shell ; spire consisting of nine or ten volutions, provided with 

 six prominent, tuberculated ribs, all the volutions having three 

 transverse, tuberculated, slightly arcuated, obtuse carina;, each 

 with three tubercles, corresponding to the number of carinae 

 which cross them ; the upper portion of the body volution 

 furnished with six compressed tubercles, and seven or eight 

 carinae, and is destitute of costa; on its lower portion ; whole 

 surface covered with minute, transverse or spiral striae ; aper- 

 ture somewhat orbicular, terminating in a short, twisted canal ; 

 outer lip expanded, undulous, but smooth on the edge ; pillar 

 lip broadly reflected on the columella. 



Found in the London Clay at Barton Cliff and Hordwell 

 Cliff. 



Genus XXVII.— NERINEA.—Z)e/AaHce. 



Shell turreted, oblong, subcanaliculated, with numer- 

 ous volutions; aperture subquadrate ; columella provided 

 with a strong fold, also one on the outer lip, and one on 

 the inner lip at the edge of the body. 



1. N. GooDHALLii Goodhali's Nerinea, pi. XXXVII.* 



fig. 2, 3. 



Nerinea Goodhallii. J. de C. Sowerby, in Geological Trans. 

 2nd Ser. IV. p. 348, pi. 23, fig. 11. G. B. Sowerby, Junr., 

 Conch. Man. fig. 374. 



Turreted, smooth ; provided with numerous concave volu- 

 tions, half as long as they are wide ; interior with three plaits, 

 one situate on the columella, one opposite it, and another above 

 it within the volution ; aperture rhomboidal. 



Fig. 3 represents a section of the shell, which exhibits its gene- 

 ric character. 



Found by Dr. Fitton in the Oxford Oolite. 



Genus XXVIIL— POTAMIS.— Srow5r„i«/-<e. 



Shell turreted ; aperture almost semicircular, but des- 

 titute of a canal in the upper angle; base contracted 

 into a short, slightly truncated beak; outer lip dilated, 

 provided with a horny operculum, in the recent con- 

 dition. 



1. P. POLITUS. — The Polished Potamis, pi. XXXVII. 

 fig. 21. 



Cerithium pulitus. Sowerby, Min. Conch. IV. p. 50, pi. 

 339, fig. 3. Cerithium tnelanoides, Ibid. II. p. 109, pi. 147, 

 fig. 6, 7. Fleming, Brit. An. p. 358. 



Subulate, smooth, shining, turreted, with obscure longitudinal 

 undulations ; body not quite one-third the length of the shell ; 

 spire consisting of ten or eleven volutions, which are very 

 convex in the centre, and separated by a very distinct suture ; 

 above the centre of the volutions is a spiral carina, which is 

 beset with large, oblong tubercles, with two or three spiral 

 tuberculated carina below, and usually with four on the body 

 volution ; aperture nearly circular, terminating in a very short, 

 slightly curved canal. 



Found in the Plastic Clay at Southfleet, Hamsay, near Croy- 

 don, Kent, and plentifully at Charlton. 



2. P. DUBius.— The Doubtful Potamis, pi. XXXVII. fig. 

 20. 



Cerithium duhinm. Sowerby, Min. Conch. II. p. 108, pi. 

 147, fig. 5. Fleming, Brit. An. p. 358. 



Subulate, turreted ; body about a third of its whole length j 

 spire consisting of ten volutions, with a spiral carina of sharp, 

 compressed, ovate tubercles near the centre, and two series of 

 lesser tubercles below; base with one or two belts of tubercles; 

 aperture nearly circular, terminating in a very short, twisted 

 canal. 



In this species the tubercles are situ.ate about one-third the length 

 of the volutions from its upper edge ; and differs from the P. poli- 

 tus in the tubercles being sharper. 



Found in the London Clay at Stubbington. 



3. P. FUNicuLATUs The Rope-like Potamis, pi. XXXVII. 



fig. 35. 



Cerithium funiculatum. Sowerby, Min. Conch, il. p. 107, 

 pi. 147, fig. 1, 2. Fleming, Brit. An. p. 358. 



Pyramidal, tapering abruptly ; body about one-third the 

 length of the shell; spire with ten or eleven volutions, flattened 

 on the sides, and separated by a shallow suture, provided with 

 four nearly equal, crenulated, rope-like carinae, the upper and 

 largest one situate near the margin of the volutions, the next 

 one the smallest, the whole being nearly equidistant from each 

 other ; aperture almost circular, ending a very short, slightly 

 twisted canal ; margin of the outer lip plain. 



The carinae in this shell strongly resemble closely knotted ropes. 



Found in the Plastic Clay at Plumstead. 



4. P. iNTERMEDius The Intermediate Potamis, pi. 



XXXVII. fig. 32. 



Cerithiuvi intermedium. Sowerby, Min. Conch. II. p. 107, 

 pi. 147, fig. 3, 4. Fleming, Brit. An. p. 358. 



Pyramidal ; body about a third of the length of the shell, 

 consisting of twelve or thirteen gradually diminishing, flat-sided 

 volutions, their superior margins closely bounded by a thick, 

 deeply crenulated carina, with four or five unequal, plain, or 

 subtuberculated and irregular carina, crossed by strong and 

 sharp lines of growth ; several elevated ridges on the base of 

 the body ; aperture subovate, rounded above, and terminating 

 below in a short, slightly bent canal. 



Found plentifully in the Plastic Clay at Charlton. 



This species may be distinguished from the P. funkulatus by the 

 irregularity of its keels. 



5. F. RIGIDUS The Rigid Potamis, pi. XXXVII. fig. 



30,31. 



Potamides rigidus. Sowerby, Min. Conch. IV. p. 48, pi. 



