152 PYRAMIDELLID^. 



upper whorls is similarly marked just above the suture ; the base 

 of the shell is almost always smooth : colour white : spire more 

 or less elongated, and tapering to a blunt extremity ; nucleus 

 smooth, higher on one side and twisted inwards : whorls b-^, 

 compressed rather than convex, shelving abruptly towards the 

 suture, each having a thickened rim round the top ; the last 

 occupies more than one-half of the shell : suture narrow, but 

 deeply excavated, scarcely oblique : mouth oval, somewhat con- 

 tracted above and much expanded below ; its length equals, and 

 in some cases exceeds, one-third of the whole spire : outer lip 

 tlexuous, slightly sinuated above, where it is gently incurved 

 on the periphery : inner Up undistinguishable and apparently 

 wanting on the upper part, not much reflected (although slo- 

 ping inwards) and nearly straight below, terminating in a rect- 

 angular base, like 0. unidentata : umbilicus none, or consisting 

 at the most of an indistinct and narrow chink, which, how- 

 ever, becomes considerably developed in aged specimens : tooth 

 short and retired, but strong : operculum flexible, with a very 

 thin flap, closely and finely striated in the line of growth, and 

 presenting the usual triangular ridge on the pillar-side and a 

 minute almost terminal spire. L. 0-125. E. 0-04. 



Var. 1. terehellum. Much larger, with an elongated spire ; 

 ribs set more obliquely, especially on the body-whorl ; tooth 

 prominent. CJiemnitzia terehellum, Philippi, Moll. Sic. ii. 

 p. 138, t. xxiv. f. 12. 



Yar. 2. suturalis. Much smaller, more cylindrical and nar- 

 rower ; ribs finer, decidedly curved, or even flexuous, on the 

 body-whorl, and occasionally covering the base. Ilissoa striata 

 (afterwards changed to B. suturalis), Phil. Z. c. i. p. 154, t. x. 

 f. 8. 



Habitat : Everywhere, in the laminarian and coral- 

 line zones ; nestling among stones and old shells, and 

 occasionally at the base of seaweeds in rock-pools at 

 spring tides. Post-glacial shell-banks in Norway, 0-100 

 feet (Sars). Extensively distributed over the North 

 Atlantic and Mediterranean, from the Loffoden Isles, 

 10-50 f. (Sars), and Bolmslan, 10-20 f. (Malm), along 

 the north coast of France (De Gervillc and others), to 

 Spczzia (J. G. J.), at depths varying from 3 to 20 f. 



