150 PYllAMIDELLIDTE. 



arc used as feelers ; the edges are often folded inwards ; it 

 ends in a needle-point : opercular lohe simple and obscure. 

 (Clark.) 



Shell cylindrical and slender, rather thin, semitransparent 

 and glossy : sculpture, numerous and close-set fine longitudinal 

 ribs, which are llexuous on the body-whorl, curved on the 

 middle ones, and obhque on those near the apex ; they dis- 

 appear towards the base ; their interstices in nearly the lower 

 half of each whorl are crossed by extremely short transverse 

 or spiral striae, of which there are from 6 to 8 rows on the 

 last whorl, 3 or 4 on the middle whorls, and 2 only on each 

 of the top -^^'liorls ; in worn specimens the decussation thus 

 produced gives a punctured appearance ; the base exhibits 

 microscoj)ic spiral lines, and the apex is quite smooth : colour 

 white : spire considerably elongated, and gradually tapering 

 to an abruptly truncated extremity ; nucleus twisted inwards : 

 whorls 7-8, convex, depressed below the suture and also on 

 the upper part of the spire ; they shelve abruptly downwards 

 towards the suture on the lower side ; each has the usual 

 thickened rim immediately below the suture ; the last occupies 

 about two-fifths of the shell : suture narrow and deep, nearly 

 straight on the upper part of the spire, becoming somewhat 

 oblique on the lower part : mouth oval, contracted above and 

 considerably expanded below ; length not one-fourth of the 

 whole spire : outer lip flexuous, retreating and forming a sinus 

 above, incurved below the periphery : inner Up extremely thin 

 on the upper part, reflected and nearly straight below : umbi- 

 licus consisting of a slight depression which ends in a small 

 narrow chink : tooth or fold none : operculum having a thin 

 flap, and obliquely striated. L. 0-165. B. 0-04. 



Yar. brevior. Proportionally smaller, with a shorter spire 

 and more convex whorls. 



Habitat : Various places from Guernsey to Shetland, 

 in from 4 to 10 f.; ^^not uncommon alive in rock-pools^' at 

 Cumbrac (Norman) . The variety is equally distributed, 

 and, according to Mr. Clark (who erroneously considered 

 it 0. clathrata) , it inhabits " a peculiar district of shelly 

 mud, between the laminarian and coralline zones in 10 

 fathoms water, off Teignmoutli.^' Sars has recorded 

 this species as occurring in a post-glacial shell-bank at 



