PROSOBRANCHIATA. 



795 



body-whorl. The whorls are convex and have a row of tubercles 

 below the suture. The outer lip is thin, the columella is smooth, 

 and there is a short wide canal. Lastly, in Rapa?ia the shell is 

 ventricose, with a short spire, the aperture is produced in front, 

 and the columella is umbilicated. The genus ranges from the 

 Cretaceous to the present day. 



Family 44. Fusid^e. — In this family the shell is elongated or 

 fusiform, dextral, or sinistral, usually without varices. The aperture 

 is moderately long, and is produced in front into a long straight 

 canal. The operculum is horny. The members of this family are 

 all marine, and the principal genera placed under this head by Zittel 

 are Fusus, Pisania, Fasciolaria, Turbinella. and Pyrula. 



In the genus Fusus the shell is spindle-shaped (figs. 704 and 

 705) and many-whorled, with an elongated straight canal. A 

 very large number of Recent and fossil forms of Fusus have been 

 recorded, and the genus has been broken up into a large num- 

 ber of minor groups or sub-genera, the characters of which cannot 

 be discussed here. Using the term 

 in its wide sense, Fusus ranges from 

 the Jurassic period to the present day, 

 attaining its maximum development in 

 the Eocene and Miocene periods. An 

 abundant form in the Red Crag (Newer 

 Pliocene) is the well - known Fusus 

 (C/irysodomus) contrarius, in which the 

 shell is reversed (fig. 705). This species 

 has now been found in the living con- 

 dition. Fusus {Chrysodomus) tornatus is 

 a common fossil in the Glacial deposits 

 of Canada (fig. 706), and still survives 

 in the neighbouring seas. 



In Pisania the shell is generally of 

 small size, with an elevated spire and a 

 short canal. The surface is smooth or 

 spirally striated, and the outer lip is 

 crenulated. The genus is exclusively 

 Tertiary and Recent. 



In Fasciolaria the shell is fusiform and 

 elongated, with smooth, angulated, or tuberculated whorls. The 

 aperture is elongated, and is prolonged anteriorly into a wide, 

 generally straight canal. The outer lip is thin, and the columellar 

 lip is tortuous, with several oblique folds. The genus ranges from 

 the Chalk to the present day. 



In Turbinella the shell is thick, with a short spire and a long 

 straight canal, the columella having several transverse folds. Lastly, 



Fig. 706. — Fusus (Chrysodomus) 

 tomatus, from the Glacial deposits 

 of Canada. 



