412 PLIOCENE MOLLUSCA. 



1898-1915. Cerithium tricinctum, A. Bell, Trans. Roy. Geol. Soc. Cornwall, vol. xii, p. 143, 1898 ; 



Greol. Mag. [6], vol. ii, p. 167, 1915. 

 1906. Potamides (Ptychopot amides) tricinctus, Cossmann, Ess. Palcocouch. coinpar., vol. vii, p. 106. 

 1912 Cerithium tricinctum, Tesch, Med. v. d. Rijks. v. Delfstoffen, no. 4, p. 76, no. 179. 

 1916. Ptychoj/otamides tricinctus, R. B. Newton, Journ. of Conch , vol. xv, pp. 70, 111, pi. iii, fig. 3. 



Specific Characters. — Shell turreted, strong in the type form; whorls 10 or 12, 

 the upper ones flattened, the lower ones becoming more or less convex, the base 

 being rounded and covered with well-marked spiral, non-granulate ridges; orna- 

 mented by three closely set rows of tubercles, connected both transversely and 

 longitudinally; spire long and subulate; suture fairly deep, slightly channelled, 

 with a fine spiral ridge above it; mouth sub-circular; canal short and narrow. 



Dimensions. — L. 40 — 54 mm. B. 13 — 16 mm. 



Distribution. — Not known living. 



Fossil : Lenham. St. Erth. Coralline Crag: Sutton, Orford 

 district, Boyton. Red Crag : Waltonian, Newbournian, Butleyan, Icenian. Isle 

 of Man. 



Miocene : Italy, France. 



Lower Pliocene : Italy. 



Upper Pliocene: Italy, Belgium, Holland. 



Var. inornata (S. V. Wood, MS., fide Van den Broeck). Plate XL, fig. 22. 



1848. Cerithium tricinctum, S. V. Wood, Mon. Crag Moll., pt. i, p. 69, pi. viii, figs. 1 b, 2. 



1882-92. Cerithium tricinctum, var. inornata, Van den Broeck, Ann. Soc. Roy. Malac. Belg., vol. xvii, 



p. 204, 1882 ; Bull. Soc. Beige Ceol., vol. vi (Memoires), p. 145, 1892. 

 1895. Potamides (Ptychopotamides) tricinctus,™?. subagranosa, Sacco, Moll. Terr. Tert. Piem., pt. xvii, 



p. 44, pi. iii, fig. 9. 



Varietal Characters .— Shell usually larger than the type, whorls more distinctly 

 convex, sometimes with 4 or 5 spiral ridges non-granulate, or but obscurely so ; 

 suture deeper. 



Dimensions.— L. 60 mm. B. 18 mm. 



Distribution. — Red Crag: Waltonian, Newbournian, Butleyan, unrecorded from 

 the Icenian. 



Var. icenica, nov. Plate XL, fig. 26. 



1833. Cerithium punctatum, S. Woodward, Greol. of Norfolk, p. 44, pi. iii, fig. 29. 



1848. Cerithium tricinctum, S. V. Wood, Mon. Crag Moll., pt. i, p. 69, pi. viii, fig. 1 a. 



1864. Cerithium punctatum, S. P. Woodward, in White's Hist, of Norfolk, ed. 3, p. 118. 



1872. Cerithium tricinctum, A. and R. Bell, Proc. Geol. Assoc, vol. ii, pp. 209, 213. 



Varietal Characters. — Shell conical, with flattened whorls and a subangulate base, 

 smaller and more fragile in the Icenian than in the typical Red Crag form; 

 granulate sculpture more distinct. 



