CERITHIUM. 257 



head rounded, never much protruded : tentacles slender, but 

 short, separated by an intermediate membrane, widely diverg- 

 ing outwards and usually curved, apparently annulated, owing 

 to their contractility; edges flattened, and scalloped or slightly 

 serrated ; tips blunt and rounded : eyes black, very small, 

 seated on bulbs outside the thickened and broad bases of the 

 tentacles : foot long, narrow, and angular, truncated ancldouble- 

 edged in front, with ear-shaped or triangular corners, pointed 

 behind. 



Shell shaped like a miniature obelisk, solid, opaque, glossy 

 and somewhat prismatic ; base slightly concave : sculpture, 

 thread-like spiral ridges, of which 4 or 5 are on the last whorl, 

 and three on each of the preceding whorls except the first two ; 

 there are also some slight and microscopic intermediate striae 

 and lines of growth ; the ridges are crossed by numerous curved 

 and fine ribs, producing nodules or small tubercles at the points 

 of intersection ; the spaces between the ribs are depressed ; 

 the base is usually devoid of all the principal markings ; the 

 first whorl and a half are smooth, and the next in succession 

 has one ridge only, besides close-set longitudinal ribs : colour 

 pale yellowish-white : spire greatly elongated ; apex bulbous 

 and twisted obliquely, slightly exceeding in breadth the first 

 regular whorl: whorls 18-20, compressed, gradually increasing ; 

 the last occupies a quarter of the shell : suture slight, defined 

 merely by the peripheral ridge : mouth bluntly rhombic, with 

 a deep and rather wide groove at the base, which bends 

 abruptly to the left, but does not form a complete canal ; the 

 entire length of the mouth scarcely exceeds one-sixth of the 

 spire : outer lip curved, thin, and indented by the spiral 

 ridges : inner lip forming a thickish glaze on the pillar, which 

 is short and nexuous : operculum thin, pale-yellowish, rather 

 coarsely striated in the "fine of growth ; spire indistinct, with 

 a minute nucleus. L. 0-8. B. 0-2. 



Habitat : Gravelly sand with mud, on the Shetland 

 fishing-banks, in 45-96 f. (M'Andrew, Forbes, Barlee, 

 and J. G. J.) ; rare. Post-glacial formation in Norway, 

 0-36 feet (Sars). Norwegian coasts, from Bergen to 

 Oxfjord, in 20-150 f. (v. Duben, Sars, Loven, M' An- 

 drew and Barrett, Danielssen, Asbjornsen, and Lillje- 

 borg) ; Villa franca (Hanley) ; United States (C. B. 

 Adams, as C. Emersonii, according to Danielssen) . 



