GASTEROPODA. 29 



of the whorls has fine encircling striae, the second circle of tubercles is not formed, or is 

 merely rudimentary, and the longitudinal ribs beneath and basal carina are both absent ; 

 the last whorl has therefore a smooth aspect, which is in striking contrast with specimens of 

 advanced age. The length of the aperture in the adult shell somewhat exceeds that of the 

 spire ; but the latter portion varies much in altitude, and occasionally exceeds the aperture 

 in length. Upon the whole, the aspect of this species varies so considerably, independently 

 of the changes produced by the stages of growth, that a considerable number are requisite 

 for its full elucidation. It accompanies P. Moreausia, but is much more rare, probably in 

 the proportion of about 1 to 10. 



The figures given by Young, Sowerby, and Buvignier, present but a remote resemblance 

 to each other and to our figures, but there cannot be much doubt of their identity. Young's 

 figure represents an individual with a spire rather depressed ; that in the ' Mineral Con- 

 chology' is from a mutilated specimen, little better than a cast. Buvignier's figure is 

 likewise imperfect, besides which, the artist appears to have represented the inner lip of a 

 true Purpura. 



Locality. Minchinhampton Common. 



This species has been found in Yorkshire only in the Coralline Oolite, where casts are 

 stated to be not unfrequent in the hard limestone. M. Buvignier's specimen is from the 

 ferruginous oolite of Vieil-St.-Remy. 



Family — Cerithiad^e. 



Cerithium, Adanson, 1757. Brug., Lam. 



Shell elongated, tuberculated or costated, seldom smooth; spire pyramidal or cylin 

 drical, composed of numerous volutions ; aperture subquadrate, terminated anteriorly by a 

 short canal, which is most frequently reflected outwards and backwards. 



Cerithium quadricinctum, Gold/. Plate IX, fig. 8. 



Cerithium giuadricinctum, Goldfuss. Petref., p. 32, t. 173, fig. 11. 

 — — Bronn. Index Palseont., p. 272. 



C. Testa conicd, anfractibus (10 — 12) quadrigonis, cingulatis, cingulis superjicialibus 

 quarternis granulatis ; granulis longitudinalibus serialis. 



Shell conical, spire obtuse, whorls (10 — 12) rather convex; encircled with four costae; 

 the costae are granulated, so as to form a longitudinal series. The whorls are narrow, 

 the height scarcely exceeding one third of the transverse diameter ; the largest specimens 

 do not exceed half an inch in length, and half of that length may be considered as the 

 average dimensions. 



