156 MALACOZOA. GASTEROPODA. PECTINIBKANCHIATi. 



upper half of the last turn, which is ventricose on the right 

 side ; the aperture roundish-oval, obtuse behind, nearly half 

 the whole length, with the peristome of uniform thickness, in- 

 complete for a short space above, a little reflexed over the um- 

 bilicus, and terminating in an inflexed fold, not rising so 

 prominently as to form a tooth, and leaving a groove from the 

 umbilicus. Length half a twelfth, breadth more than half the 

 length. 



This species, although destitute of a tooth, has the general 

 conformation of the genus. The peristome not being com- 

 plete, it cannot be referred to Rissoa. It closely resembles 

 Odostomia spiralis, but differs, as Montagu has remarked, in 

 the volutions being more rounded, in the ribs being coarse, 

 and in being destitute of the tooth-like plication on the co- 

 lumella. The mouth is large, the spiral striae not forming a 

 ridge along the suture. 



Found by me, in September, 1842, among shell sand, on 

 the beach, between the mouths of the Dee and the Don. 



Turbo semicostatus. Mont. Test. Brit. 326. PI. 1. f. 5. — Pyramis 

 semicostatus. Brown, Brit. Sh. PI. 50. f. I, 2. — Cingilla semicos- 

 tata. Flem. Brit. Anim. 307. 



7. Odostomia plicdtula. Plicatulate Odostomia. 



Shell ovato-conical, of five rather thick, opaque, glossy 

 turns, which are distinctly separated by a deep suture, flat, 

 finely plicato-striate transversely, the last turn with the plicae 

 ending about the middle, and succeeded by three or four 

 spiral striae, the terminal part of the turn plain ; the mouth 

 ovate, subangulate anteriorly, acute behind, less than half the 

 whole length, with the peristome rather thin ; a very slight 

 plait on the columella ; no umbilicus or groove. Length 

 nearly half a twelfth, breadth about half the height. 



Similar in form to Odostomia interstincta, but differing in 

 having the turns more flattened, the plicae more numerous, 

 the columellar plait smaller, and in having the spiral striae on 

 the last turn. 



Found by me, in September, 1842, among shell sand, on 

 the beach, near the Broadhill. 



8. Odostomia Marionce. Marion's Odostomia. 



Shell ovato-conical, of five convex, thin, transparent, rather 

 glossy turns, which are finely plicate transversely, and delicately 

 striate spirally, the upper margin of each in the form of a plait- 

 ed rib ; the mouth ovate, nearly half the whole length, with 



