CERITHIUM. 259 



SHELL forming an extremely elongated pyramid with a 

 narrow base, rather solid, opaque, having scarcely any gloss : 

 sculpture, thread-like spiral ridges, of which from 8 to 10 are 

 on the last whorl (4 above the periphery, and the rest below 

 it), 4 on each of the preceding 7 or 8 whorls, 3 on each of the 

 next two whorls, 1 or 2 on each of the upper two whorls, where 

 they cease ; the ridges are crossed by strong longitudinal ribs, 

 which make the former nodulous ; of these ribs there are about 

 20 on the penultimate whorl ; they do not extend to the outer 

 lip nor below the periphery; besides the above sculpture, close- 

 set longitudinal striaB are perceptible with a magnifying power, 

 and some of the ribs (but never more than one on a whorl) are 

 varicose or unnaturally distended ; the first whorl and a half 

 are smooth and glossy : colour chestnut or reddish-brown of 

 various shades, often dusky ; the nodules sometimes whitish 

 from friction : spire drawn out to a considerable length ; apex 

 bulbous, and twisted obliquely : whorls 15-16, rather convex ; 

 rate of increase very gradual, the last whorl equalling nearly 

 one-third of the shell: suture deep, defined by the peripheral 

 ridge : mouth triangular ; basal groove rather wide, but not 

 deep, turning abruptly to the left, not exhibiting any notch on 

 the outside; the entire length of the mouth does not much 

 exceed one-fifth of the spire : outer lip rounded, and slightly 

 reflected ; inside indented by the spiral ridges : inner lip form- 

 ing a fine glaze, which is thicker on the pillar ; the latter is 

 very short and flexuous : operculum stouter than in the last 

 species, obliquely and coarsely striated ; its spire is composed 

 of about half a dozen whorls, which are defined by an imbri- 

 cated or overlapping edge. L. 0'5. B. 0-125. 



Yar. 1. simplex. Shell rather thinner, and glossy, without 

 any varix ; colour yellowish- white, the ridges marked by 

 purplish-brown lines. 



Yar. 2. lactescens. Becoming milk-white. 



HABITAT : Very common in the littoral and lamina- 

 rian zones, on the southern arid western coasts of England, 

 Wales, and Scotland, as well as all round Ireland; 

 Sandwich (Montagu). Var. 1. Sark (Earlee); Guernsey 

 and Herra, living under stones and in rock-pools at low- 

 water mark, and dead in 20 f. (J. G. J.) : this is more 

 frequent than the typical kind in the south of Europe. 



