462 



MOLLUSCA 



SUB-KINGDOM VI 



attended with great difficulty, since they frequently possess nearly identical- characters 

 in common, differing mainly in the operculum, which is not preserved fossil. 



FIG. 893. 



Sigaretus haliotoideus, 

 Linn. sp. Miocene; 

 Grund, Hungary. 



A , Natica millepunctata , Lain. Plio- 

 cene ; Monte Mario, near Rome. B, 

 Operculum of N. multipunctata, S. 

 Woodw. Crag; Sutton. 



FIG. 895. 



Natica (Ampullina) patula, 

 Lam. Calcaire Grossier ; 

 Damery, near Bpernay. 



Sigaretus, Lain. (Fig. 893). 

 Spire very low, with 

 distended ; operculum 



Natica, Lam. (Figs. 

 pyramidal, smooth and 



FIG. 896. 



Natica (Amaur- 

 opsis) Willemeti, 

 Lam. Calcaire 

 Grossier ; Damery, 

 near Epernay. 



FIG. 897. 



Natica (Amauropsis) bul- 

 biformis, Sowb. Upper 

 Cretaceous ; St. Gilgen 

 on Wolfgangsee, Austria. 



Shell depressed, auriform, spirally striated or furrowed, 

 rapidly widening whorls. Aperture greatly 

 horny. Tertiary and Recent. 

 894-897). Globose, semi-globose, ovate or 

 lustrous, rarely spirally striated, umbilicate 

 or not. The umbilicus, when present, often 

 partially or entirely filled with callus. 

 Aperture semi - circular or oval. Outer lip 

 sharp; inner lip 

 thickened by a callus. 

 Excessively abundant 

 from the Trias onward. 



Sub -genera : Ampul- 

 lina, Lam. (Fig. 895) ; 

 Amauropsis, Morch (Figs. 

 FlG gyy 896, 897) ; Amaura, Moll.; 



Deshayesla c'ochlearia, %*> Cernma Gray ; 

 Brongt, sp. Oligocene ; Neventa, Risso ; Maimlla, 

 Monte Grumi, near Schum., etc. 



Vicenza. 



Raul. 



Miocene 



(Fig. 898). Like Natica, but inner lip with thick callus and denticulated, 

 and Pliocene. 



Family 6. Xenophoridae. Deshayes. 



Shell turbinate, without nacreous layer ; whorls flat, often covered with agglutinated 

 foreign bodies. Base conical or fiat, with a sharp peripheral keel. 

 Aperture obliquely quadrilateral. Operculum horny. Silurian 

 to Recent. 



The Xenophoridae are an ancient family, the modern re- 

 presentatives of which have acquired a high differentiation. 

 The radula is like that of the Gapulidae, Littorinidae, and 

 Strombidae, not like that of the Trochidae. The earlier forms, 

 encountered in the Silurian, present a great superficial re- 

 semblance to the Palaeozoic Trochus species. 



Eotrochus, Whitf. (Fig. 899). Thin-shelled, turbinate, widely \ 

 umbilicate. Whorls flat, rarely with agglutinated foreign particles. 

 Base concave, its periphery formed by a compressed lamellar belt. 



Xenophora heiiacua, d'Orb. 

 1 * 



Silurian to Recent. 



