GASTEROPODA. 



15 



Fig. 394. — Cyprcea eUgans. 

 Eocene Tertiary. 



Fam. 7. NATICIDJ5. — Shell globular, of few whorls, with a 



small spire ; outer lip acute ; inner lip (pillar) often callous. 



Foot very large ; mantle - lobes hiding 



more or less of the shell. This family 



is stated to commence in the Upper Si- 

 lurian rocks ; but there is considerable 



uncertainty as to the true affinities of 



the Palaeozoic fossils which are referred 



here. The most important fossil genus 



is Natica itself. 



The shell in Natica (fig. 395) is thick, 



smooth, and polished, often Avith coloured 



markings. The inner lip is callous, and 



the shell is umbilicated. Fossil Naticm 

 have been described from the Upper Silu- 

 rian, Devonian, Carboniferous, and Permian rocks ; and they 

 are very abundant in all the Secondary and Tertiary for- 

 mations. There is great doubt about the true affinities of 

 the more ancient shells referred here ; 

 and the typical Natica:, with a wide 

 umbilicus and a twisted columella, are 

 represented by very few forms even in 

 the Cretaceous period. Naticoj^sis (fig. 

 397, b) of the Carboniferous; Naticella 

 of the Trias ; the Jurassic Uuspira, with 

 its elevated spire and angulated whorls ; 

 and the Tertiary Globulus, are close allies 

 of Natica proper. Narica (fig. 397, c), 

 with its spirally-striated shell, and Am- 

 aura, range from the Cretaceous to the present day. Desha- 

 yesia, of the Eocene, is a link between the Naticiclce and 

 Neritidce ; and Sigaretus (fig. 397, a), ranging from the Eocene 

 to the Eecent period, is easily recognised by its wide aperture 

 and minute spire. 



Fam. 8. Pyramidellid^. — Shell turreted, with a small 

 aperture ; sometimes with one or more prominent plaits on 

 the columella. Operculum horny and imbricated. The 

 Pyramidellicke commence in the Lower Silurian rocks, and 

 appear to be on the decline at the present day. The chief 



Pig. 395. — Natiai clausa. 

 Post- Pliocene. 



