MALACOZOA. GASTEROPODA. PECTINIBRANCHIATA. 153 



direct on the inner, leaving a very small cavity ; the colour 

 hyaline-white, the last turn brownish-red around the mouth. 

 Length a twelfth and a fourth, breadth a fourth of the height. 



This shell is nearly allied to Rissoa rubra, which however 

 differs in being less attenuated, with the mouth rounder. It 

 resembles Rissoa striata in form, but is much more elongated, 

 and, being destitute of markings, cannot be mistaken for that 

 species. 



Found, in August, 1842, by Miss Anne Macgillivray, in 

 shell sand on the beach between the mouths of the Dee and 

 the Don. 



Family IV. — Tornatellina. 



Shell spiral, ovate, oblong, or turrite, with the aperture 

 oblique, ovate, oblong, or narrow, entire anteriorly, nar- 

 rowed behind by the convexity of the last volution, the 

 inner lip ending in an oblique plait on the columella. 



The structure of the animals of this group seems to 

 be little known ; but any shell belonging to it may be 

 at once known by comparing it with the above definition. 



Genus I. Odostomia. 



Shell ovato-conical, with the apex rather obtuse or 

 mammillate, the aperture suboval, with the peristome 

 incomplete behind, and having a tooth-like plait on the 

 columella. 



This genus, instituted by Dr. Fleming, who named it 

 by its most prominent character (odovs, a tooth, and scofxa, 

 mouth), closely resembles Rissoa, and is composed of 

 similarly minute shells, which are to be looked for on 

 the sandy shores. Montagu, in describing Turbo spiralis, 

 observes, "the pillar-lip turns inward and forms an 

 apparent small denticle, which in fact is a plication or 

 ridge, that runs spirally some way up the columella ; a 

 character in this and the three following species (Tur- 

 bines interstinctus, unidentatus, and plicatus), not subject 

 to vary like the denticulations in some other shells, but 

 is the constant formation of the Columella, occasioned 

 by the intortion of the pillar lip, as in the Voluta tor- 

 natilu ; to which genus they become a sort of link." 



