134 PYRAMIDELLID^. 



13. O. unidenta'ta"^, Montagu. 



Twrho unidentatus, Mont. Test. Br. (ii.) p. 324. 0. unidentata, F. & H. 

 iii. p. 264, pi. xcv. f. 7, 8. 



Body clear bluish-white : snout compressed, bevelled at the 

 margin, and truncated in front: tentacles short, broad, awl- 

 shaped, " setose" [?], blunt, with a fine transparent line down 

 the middle of each : eyes close together, sunken in the mem- 

 brane which connects the tentacles ; foot short, truncated in 

 front and slightly eared, sloping behind to a broad, obtuse, 

 lance-shaped point ; sole in front flake-white, behind hyaline, 

 with a fine longitudinal line along the centre of the posterior 

 half ; it is divided from the upper disk by a shallow groove, 

 giving the foot a labiated aspect. (Clark.) 



Shell, a rather long cone with a broad base, solid, almost 

 opaque, and glossy : sculpture, microscopical and slight but 

 close-set spiral striae, and a more or less distinct keel round 

 the periphery, as well as at the base of each of the upper 

 whorls : colour milk-white, with a bluish tint in immature 

 specimens : spire shortish ; nucleus exposed, twisted in some 

 specimens backwards, and in others forwards : wJiorls 6, besides 

 those of the embryonic nucleus ; they gradually enlarge, and 

 are nearly flat ; the last equals in length the rest of the spire ; 

 suture narrow but distinct, defined above by the peripheral 

 keel, from which it slopes downwards : mouth squarish, ex- 

 panded and forming nearly a right angle at the inner base ; 

 its length is about a third of the whole spire : outer Up nearly 

 semicircular, incurved (but not much) just below the periphery: 

 inner lip extremely thin on the upper part, where it adheres 

 to the pillar but does not join the outer lip, reflected and nearly 

 straight on the lower part, the angle at the base being well 

 marked: umbilicus none, although there is sometimes a small 

 chink : tooth large, strong, prominent and consincuous, placed 

 as in several of the species last described; it is continued 

 throughout the spire : operculum as in 0. cono'idea. L. 0*2. 

 B. 01. 



Yar. elata. Spire more elongated, and base narrower. 



Habitat : Under stones at low-water mark of spring 

 tides, and on old oyster- shells and Pec ten maxhnus in 

 the laminarian and coralline zones, on every part of our 



* Single-toothed. 



