3S8 MOLLUSCA. CERITHIAD^. Potamidum- 



3. Cftinatum. — Conical, elongated, with two obtuse crenulated transverse 

 ridges upon each whorl ; upper part of each whorl thickened and tuberculated ; 

 mouth squarish ; base smooth. Sower. Min. Conch, t. cxxviii. — In Plastic 

 Clay. 



4. C. funiculatum. — Pyramidal ; sides straight ; whorls with four, nearly 

 equal, crenulated carinse on each ; base with several plain elevated ridges. 

 Sower. Min. Conch, t. cxlvii. f. 1, 2. — Plastic Clay. 



5. C. intermedium. — Pyramidal, sides straight ; whorls with a largely cre- 

 nulated margin, and five or six unequal carhire on each ; base with several 

 elevated ridges. Soivei: Min. Conch, t. cxlvii. f. 3, 4. — Plastic Clay. 



6. C. dubium. — Turrited ; whorls with a row of compressed tubercles near 

 the middle, and two transverse rows of lesser tubercles below ; base with one 

 or two rows of tubercles. Sower. Min. Conch, t. cxlvii. f. b.— London Clay. 



7. C. melanoides. — Turrited, obscurely longitudinally undulated; whorls 

 convex, bearing above the middle a large tuberculated carina, below with two 

 or three transverse tuberculated carinse ; beak very short. Sower. Min. 

 Conch, t. cxlvii. f. 6, 7 ; and t. 339. f. 3 — Plastic Clay. 



8. C. rigidum Subulato-conical, nearly smooth ; lower whorls surrounded 



by a keel near their upper parts. (Buccinum. rig. Brander, f. 43.)— Potami- 

 dis reg. Sower. Min. Conch, t. ZZQ.—Londo^i Clay. 



9. Cconcavum. — Subulato-conical; spirally striated ; whorls rather concave 

 towards the upper part; costated; costte obscure, arched, with a slight emi- 

 nence above the middle of each ; base with one or two granulated carinse, 

 convex ; lip enlarged below, with a small groove in its upper angle — Pota- 

 mides con. Sower. Min. Conch, t. cccxxxix. f. 1, 2 — Upper marine formation. 

 Isle of Wight. 



10. C. margaritaceum. — Conical, turrited, five close rows of bead-like gra- 

 nules surround each whorl, the first and fourth rows minute, the fifth larger 

 than the other two ; lip expanded, plicated ; pillar recurved, obtusely cari- 

 nated. — Potamides marg. Sower. Min. Conch, t. cccxcix. f. 4 — Upper marine 

 formation., Isle of Wight, 



11. C. plicatum Subulato-conical, or subcylindrical ; whorls longitudinal- 

 ly plaited, transversely sulcated and striated ; sulci three or four ; base con- 

 vex ; lip crenulated — Potamides plic. Sower. Min. Conch, t. cccxl. f. 2.— Up- 

 per marine formation. Isle of W^ight^ 



12. C. duplex Subulato-conical, with two rows of tubercles upon the up- 

 per, and three upon the lower whorls ; upper rows of tubercles largest ; sides 

 of the whorls Hat ; base flat, with two caiinoe near its edge ; beak short, inner 

 edge rising upon the pillar — Potamides duplex, Sower. Min. Conch, t. cccxl. 

 f. 3 Upper marine formation. Isle of Wight. 



Gen. potamidum. — Canal very short ; aperture entire re- 

 trally ; outer-lip patulous. 



1. P. acutum Conical, turrited ; whorls convex, bicarinated ; carinDe acute ; 



base convex, bistriated ; aperture orbicular, with a narrow short beak, Sower. 

 Min. Conch, t. cccxli. f. 2 — Lower fresh u-ater formation. Isle of Wight. 



2. P. ventricosum Conical, turrited; whorls ventricose, costated, trans- 

 versely striated ; striae two or three upon each whorl, most elevated upon the 

 costse ; aperture orbicular, with an extremely short beak — Sower. Min. Conch, 

 t. cccxli. f. 1 Fresh water formation. Isle of Wight and Cowes. 



