22 LITTORINID.E. 



11. R. costa'ta^^ Adams. 



Turho costatus, Ad. in Tr. Linn. Soc. iii. p. 65, t. 13. f. 13, 14. B. costata, 

 F. & H. iii. p. 92, pi. Ixxviii. f. 6, 7. 



Body clear-white : snout long, cloven vertically at the ex- 

 tremity, and exposing the buccal disk, which is pale-red : ten- 

 tacles slender, flattened, apparently not setose : eyes large : 

 foot long, rounded in front, where it has a snow-white mark 

 like the letter Y, behind which it is constricted at the sides 

 and di\-ided across, thence somewhat expanding, and tapering 

 to a blunt point behind ; the lower lip or edge of the foot in 

 front extends much beyond the upper lip : opercular lobe dilated 

 into rounded lateral wings : appendage single, distinct. 



Shell oblong and slender, obliquely twisted, solid, nearly 

 opaque, glossy when inhabiting clean ground, but usually lus- 

 treless : sculpture, ridge-like, sharj), high-shouldered, and flex- 

 uous longitudinal ribs, of which there are 9 on the last whorl, 

 10 on the penultimate, 11 on the next, and 12 on the suc- 

 ceeding whorl, where they mostly disappear ; the ribs on the 

 body-whorl do not extend quite to the base, being cut off by 

 a strong (sometimes double) keel or ridge which winds si^iraUy 

 round that part ; between this keel and the mouth is a deep 

 groove or depression caused by the prominence of the keel ; 

 the labial rib is thicker than any of the rest, and its inside 

 edge is flattened and finely notched; the last four or five 

 whorls are covered with numerous delicate spiral strite, which 

 cross the ribs ; the top whorls are quite smooth : colour clear- 

 white, with a slight golden tinge : spire long and pointed : 

 whorls (5, compressed, the last occupying three-fifths of the 

 spire, and the first being minute and rounded : suture deep : 

 mouth roundish-oval, expanding outwards : outer and inner 

 lips sinuated, continuous, and forming a complete and slightly 

 elevated rim round the mouth : opercidum ear-shaped, thin, 

 yellowish-horncolour, with a small excentric spire, and finely 

 striated. L. 0-125. B. U-06. 



Habitat : Coralline and lower part of the laminarian 

 zones ; more generally distributed in the south than in 

 the north. Dr. Gordon and Mr. Dawson find it on the 

 coast of Aberdeenshire ; I have dredged it in the He- 



* Eibbed. 



