MA1AC0Z0A. GASTEROPODA. PECTIN1BRANCHIATA. 149 



6. Rissoa pdrva. Thick-lipped Ribbed Rissoa. 



Shell ovato-turrite, rather thick, nearly opaque, glossy ; the 

 spire nearly half as long again as the last turn, directly taper- 

 ing, rather obtuse ; the whorls six, rounded, with strong, con- 

 vex, slightly waved, transverse ribs, but without spiral striae ; 

 the ribs of the last whorl ten or twelve, not reaching the mouth ; 

 the suture distinct, the aperture roundish-ovate, the outer lip 

 thickened externally by a broad convex rib, the inner a little 

 reflexed, and leaving a groove behind, but no perforation ; the 

 colour white, tinged with red, or reddish with the ribs white. 

 Length an eighth of an inch, breadth nearly half the length. 



It varies in colour, number, and extent of the ribs. 



Among shell sand on the beach between the Dee and the 

 Don ; also in Cruden Bay, at Fraserburgh, and Gamrie. 



Turbo parvus. Mont. Test. Brit. 310. — Rissoa parva. Johnst. 

 Berw. Trans, iii. 272. — Cingula parva. Flem. Biit. Anini. 306. — 

 Turbo quinque anfractibus subcarinatis, apice purpureo, apertura 

 ovali. Walker, Test. Min. Rar. 12. PL 2. f. 43. 



5. Rissoa alba. Thin-lipped Ribbed Rissoa. 



Shell ovato-turrite, rather thin, semitransparent, glossy ; the 

 spire nearly half as long again as the last turn, directly taper- 

 ing, rather obtuse ; the whorls six, rounded, with convex, 

 slightly waved transverse short ribs, those of the last whorl 

 from twelve to sixteen, not extending beyond the middle ; the 

 suture very distinct ; the aperture roundish, the outer lip thin, 

 the inner a little reflexed, and leaving a slight groove ; the 

 colour white, reddish, or pale brown, sometimes with brown 

 bands. Length an eighth of an inch, breadth less than half 

 the height. 



Nearly allied to Rissoa parva. It varies greatly in the ex- 

 tent and number of the ribs. 



Among sand and shells sent by Mr. Alexander Murray from 

 Fraserburgh, Cruden, and Ugie, in 1 842 ; also on the beach at 

 Aberdeen. 



Turbo albus. Adams, Linn. Trans, iii. 66. PI. 15. f. 17, 18. — 

 Rissoa alba. Forbes, Mai. Mon. 16 — Cingula alba. Flem. Brit. 

 Anim. 309. 



6. Rissoa semistridta. Semistriated Rissoa. 



Shell ovato-conical, pellucid, spirally striated, glossy ; the 

 spire shorter than the last turn, directly tapering to a rather 

 obtuse point ; the whorls five, rather convex, the last sulcato- 

 striated anteriorly ; the suture distinct ; the aperture roundish- 



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