792 



DIVISIONS OF THE GASTROPODA. 



Fig. 698. — Cassis canalicula 

 tus. Recent. 



the Chalk to the present day, differs from the Cowries in having 

 a cone-shaped shell, with a short but visible spire. 



Family 37. Cassidid^. — In this family the shell is ventricose, 

 with a short spire and a large body-whorl. The aperture is long 

 and narrow, notched in front, or with a short recurved canal (fig. 

 698). The inner lip is callous, and the 

 outer lip is thickened and often plaited or 

 denticulated. The members of this family 

 are all marine, and the oldest forms belong- 

 ing to it appear in the Upper Cretaceous 

 rocks. 



The genus Cassis (fig. 698) comprises the 

 " Helmet-shells," distinguished by their short 

 spire, large body-whorl, elongated aperture, 

 short recurved anterior canal, and expanded 

 inner lip. The earliest forms of Cassis ap- 

 pear in the Eocene Tertiary, and the genus 

 still survives. Cassidaria (Upper Cretaceous 

 to Recent) closely resembles Cassis, but the 

 canal is elongated and produced. Lastly, Oniscia, with the same 

 range in time as Cassidaria, has the aperture truncated in front, 

 with a straight canal or notch. 



Family 38. Doliid^e. — In this family the shell is thick and ven- 

 tricose, with a large body-whorl and a wide oval aperture. The 

 whorls are longitudinally ribbed, and there 

 is a short anterior canal, which may be 

 straight or recurved. This family includes 

 only the genus Dolhim, the species of which 

 are marine. The fossil forms are chiefly 

 Tertiary, but a Cretaceous species of the 

 genus is known. 



Family 39. Ficulid^:. — In this family 

 the shell is thin and ventricose, spirally 

 ribbed or cancellated (fig. 699). The aper- 

 ture is of large size, and is prolonged in 

 front into a long canal. This family in- 

 cludes only the genus Ficula (Pyrula in 

 part), in which the shell is pyriform, with 

 a very large body- whorl and a ■ short spire, 

 and with a sharp outer lip. The recent 

 species of Ficula are inhabitants of the sea, and the earliest fossil 

 forms of the genus appear in the Cretaceous rocks. 



Family 40. Tritoniid/e. — In this family the shell is spindle- 

 shaped, with a straight or somewhat bent canal. The whorls are 

 often adorned with varices, and a horny operculum is present. 



Fig. 699. — Ficula {Pyrula) 

 reticulata. Miocene Ter- 

 tiary. (After Zittel.) 



