ODOSTOMIA. 165 



extremity, which is rounded when at rest, and apparently 

 truncated when carried before the foot on the march : tentacles 

 short, very bluntly pointed and leaf-like, having large and 

 extremely flexible lateral membranes which coalesce for half 

 their height, and are capable of instantaneously assuming 

 various shapes : eyes at a little distance from the internal line 

 of the tentacular bases : foot truncated in front, very slightly 

 auricled, narrow, not very long, attenuated and tapering be- 

 hind to a rounded broad termination : opercular lobe obscure. 

 (Clark.) 



Shell forming a greatly elongated cone, rather solid, nearly 

 opaque, and glossy : sculpture, strong, narrow, and close-set 

 longitudinal ribs, from 20 to 2b on the last whorl ; they are 

 more or less curved or flexuous, and placed obliquely, and 

 they terminate abruptly a little below the periphery, the base 

 being perfectly smooth ; although no other sculpture is visible 

 with a low magnifying-power, the whole surface of a live spe- 

 cimen exhibits under the microscope extremely numerous spiral 

 lines ; the first whorl is glabrous : colour milk-white, with a 

 slight bluish tinge in live specimens : spire tapering to a 

 rounded point ; embryonic nucleus as in the last species : 

 whorls 12 (exclusive of the nucleus), moderately convex, and 

 gradually enlarging ; the last occupies from a fourth to a third 

 of the shell : suture narrow and deep, slightly oblique : mouth 

 irregularly rhomboidal, longer and more expanded at the base 

 than in 0. rufa, but similar in all other respects : outer lip 

 gently rounded, except under the periphery, where it is very 

 slightly incurved and shelves outwards : inner lip forming a 

 thin glazing or layer on the upper slope of the pillar, very 

 little reflected and nearly straight below, where it is more ex- 

 tended than in the last species : umbilicus none : tooth usually 

 wanting ; but in some specimens an obscure tubercle may be 

 detected on the upper part of the pillar, far within the mouth : 

 operculum as in the last two species, sometimes slightly notched 

 on the inner side to accommodate the tooth when present. 

 L. 0-35. B. 0-1. 



Var. pauUula. Dwarfed and depauperated. 



Habitat : English, Bristol, and St. George's Chan- 

 nels, all Ireland, and the west coast of Scotland, as far 

 north as Loch Ewe; Aberdeen (Macgillivray) ; Dunbar 

 (Laskey,j?fife Brown); Sandwich (Walker); Roach River* 



