RISSOA. 35 



mouth, aud in the striae being cancellated instead of 

 punctured. 



This is probably the R. Guerinii of Recluz. The same 

 author also described it as R. lilacina, Delle Chiaje as 

 Turbo Rissoanus, Chiereghini as T. Mavors, Renier as 

 T. amethystinus, and Potiez and Michaud as R. punctata. 



17. R. costula'ta *, Alder. 



B. costtdata, Aid. in Ann. & Mag. N. H. xiii. p. 324, pi. yin. f. 8, 9 ; F. 

 & H. iii. p. 103, pi. lxxvii. f. 4, 5. 



Body yellowish, tinged with brown in front : snout rather 

 long, wrinkled, and cloven at its extremity : tentacles thread- 

 shaped, slender, retractile, finely setose, sulphur-coloured, with 

 a greenish hue or vein down the middle of each : eyes on small 

 bulgings of the tentacles, at their outer bases : foot rounded in 

 front, divided across in the middle, so as to make the anterior 

 and posterior portions appear separate, bluntly pointed behind; 

 posterior half of the sole grooved lengthwise ; appendage white, 

 retractile. 



Shell conic-oblong, somewhat spindle-shaped in consequence 

 of the apex being pointed and the base narrower than the 

 middle, rather solid, nearly opaque, more or less glossy ; sculp- 

 ture, strong, prominent, and nearly straight longitudinal ribs, 

 10 of which are on the penultimate whorl, those on the last 

 whorl usually disappearing towards the mouth ; there are none 

 on the upper three or four whorls, which are quite smooth ; 

 near the mouth is a rib, much larger and broader than any of 

 the rest ; the ribs on each whorl are either continuous or 

 arranged alternately, so as to appear dovetailed; the spaces 

 between the ribs and the space near the mouth are covered 

 with fine and rather numerous transverse or spiral striae, the 

 interstices of which are delicately and closely cancellated, es- 

 pecially at the base of the shell : colour pale-yellowish or dirty 

 white, often tinged with lilac, or streaked lengthwise with 

 reddish -brown, sometimes pure- white; the ribs are mostly of 

 a lighter hue -or whitish, and are therefore conspicuous ; the 

 inside edge of the mouth is nearly always lilac or reddish-brown; 

 occasionally the whole surface, except the labial rib, is orna- 

 mented by longitudinal zigzag streaks of reddish-brown, and 



* Slightly ribbed. 



