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Genus 2. OLIVA, Bruguiere. 



Animal ; disc widely expanded, reflected on either side over the 

 anterior portion of the shell, forming a capacious fold, some- 

 times rounded, sometimes acuminated behind, front extremity 

 furnished with a pair of icing-like lobes, anterior to the head; 

 head very small, tentacles thickened about half-way, at the 

 summit of which thickened portion is the eye : mantle small, 

 hind extremity furnished with a filament or cord ivhich passes 

 into a groove in the spire of the shell, front portion forming an 

 ample siphon for conveying the water to the branchial cavity, 

 with a flowing triangularly pointed appendage behind it. 



Shell; polished, more or less cylindrical, emarginated at the base ; 

 spire short, sharp at the apex ; whorls closely convoluted, ivith 

 a deep narrow channel round the spire, in the place of the 

 suture; aperture narrow, extending nearly the length of the 

 shell; columella obliquely grooved, terminating ivith a callosity, 

 lip simple. 



The Olives were arranged by Lamarck in the same family with the 

 Cowries on account of their polished exterior ; they have been removed to 

 the Pnrpurifera, because of their affinity with Ancittaria and Eburna. 

 The whorls of the shell are convoluted on nearly the same vertical plane 

 with the spire, and the columella is obliquely grooved, as if it had been 

 bound, as it were, with cords, sufficient to swell the base into a callosity ; 

 the most striking character, however, is the presence of a deep narrow 

 groove, encircling the spire in the place of the suture, the use of winch I 

 have now to explain. 



The enamelled exterior of the Olive-shell indicates that it is more or less 

 enveloped, like the Cowrey, with a portion of the animal ; but it is not 

 covered by the mantle, it is protected by a modification of the disc ; the 

 calcifying organ of these mollusks differs both in structure and function. 

 In the Cowrey, the office of calcification is performed by a lobate extension 

 of the mantle from either side of the aperture, sufficient to cover the shell, 

 and only retracted under a state of alarm. In Oliva the mantle is limited 

 to the interior and aperture of the shell ; it appears to be furled over the 

 edge of the lip, and is held, as it were, in a state of tension by a cord or 

 filament passing from the posterior extremity into a deep narrow channel, 

 which is excavated round the spire of the shell in place of the suture. The 

 result of this difference in the condition of the calcifying organ, is, that in 



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