288 GASTROPODA. [PeclinibrancJiia. 



system, much produced in front, where it is furnished with a fold 

 (propodium) covering the head and anterior margin of the shell ; oper- 

 cuiigerous lobe very ample, partially enveloping the shell ; mantle 

 enclosed. Jaws corneous, waved or tessellated, subtrigonal. Central 

 tooth of the radula trapezoidal, generally tricuspidate ; lateral teeth 

 with a central large and smaller cusps ; inner marginals simple or 

 bifid ; outer marginals simple. 



Shell turbinate, subglobose or auriform, the spire usually short ; 

 aperture entire, without canal or sinus ; the outer lip sharp, not 

 reflected or margined ; the inner lip callous, more or less reflected 

 over the umbilicus. Operculum calcareous or corneous, paucispiral. 



The animals of Naticidce, characterized by the cephalic disc forming 

 the propodium, are completely retractile within the shell in the typical 

 Natica, but not retractile in some other forms. The nidus is unlike 

 that of any other mollusc in form and composition, being built up 

 largely of the sand of the sea-bottom, agglutinated into a strap, form- 

 ing part of a circle, and provided on one side with a constriction or 

 rim ; the walls contain the eggs, arranged in quincunx order. 



The Natica is an active animal, carnivorous and very predaceous, 

 living in sandy places, where it hides under the surface, and burrows 

 for bivalves ; these it pierces with its tongue, boring a round hole,, 

 generally near the beaks, where the shell of the victim is thinnest. 



KEY TO GENERA. 



A. Operculum calcareous . . . . . . . . . . NATICA. 



B. Operculum horny. 



a. Aperture not very large, columella nearly straight . . POLINICES. 



n/i. Aperture very large, columella curved, S-shaped . . AMPULLINA. 



Genus 1. NATICA, Scopoli, 1777. 



Natica, Scopoli, Introd. Hist. Nat., 1777, 392. Type : Nerita vitellus, L. 

 Xatica, Scopoli: Bruguiere, Enc. Meth., i, p. xvi, 1789; Lamarck, 

 Prodrome, 1799, 77. Cochlis, Bolten, 1798. Nacca, Risso, 1826. 



Animal with large cephalic lobe, truncated in front, sub- 

 quadrangular. 



Shell oval-globular, porcellanous, solid, generally smooth, covered 

 by a fine epidermis, which is transparent and generally not very 

 persistent ; umbilicated, or umbilicus more or less filled with callus ; 

 aperture semilunar, vertical, the outer lip simple. Operculum large, 

 semilunar, paucispiral, calcareous. 



The species are numerous ; mostly inhabitants of the warm seas, 

 in all quarters of the globe. The genus first appeared in the Jurassic 

 formation. The fossil forms are remarkable for the persistence of 

 their colours. 



Vernacular Name. Necklace-shell. 



KEY TO SPECIES. 



A. Umbilicus with a white, central, entering callus ; shell of moderate 



size . . . . . . . . . . . . . . zdandica. 



B. Umbilicus partly covered by a brown not entering callus ; shell 



small . . australis. 



