20 



GASTEROPODA. 



The genus Vermdus comprises tubular sliells, the chief 

 interest of Avhich is the strong resemblance which they show 



Fig. 402. — TurriteUa angu- 

 lata. Neocomian. 



Fig. 4u3. — Siliqunria 

 angninu. Pliocene and 

 Recent. 



Fig. 404. — Sridiiria 

 Grccnktndica. Post- 

 Pliocene and Recent. 



to the Annelidous genus Scrpnia. The shell is attached, and 

 though regularly spiral when young, is always irregular in 

 its growth when adult. The fossil species are best distin- 

 guished from Serjmla by the fact that the tube is repeatedly 

 partitioned off by calcareous septa as the animal grows. 

 It is, however, often a matter of extreme difficulty to deter- 

 mine whether a given specimen be a Vcrmctus or a Serpula. 

 Fossil Vermeti are known from the Lower Cretaceous up- 

 wards. Siliquaria (fig. 403), dating from the Eocene Ter- 

 tiary, resembles Vcrmctus in most respects, but the tube has 

 a continuous longitudinal slit. These two forms are often 

 regarded as a separate family ( Vcrmctickv). In Caxum, again, 

 also often looked upon as forming with some allied types a 

 distinct family (Cccculcc), the shell is at lirst discoidal, but 

 becoming decollated with age, has the form of a curved 

 cylindrical tube when adult. The genus commences in the 

 Eocene Tertiary. 



The genus Scalaria, comprising the Wentletraps, is the 

 type of another group now commonly looked upon as a dis- 

 tinct family (Scalidce or Scalaridce), the characteristics of the 

 section being the possession of a spiral and turreted shell, 

 usually marked with longitudinal ribs, and having the aper- 

 ture round and with an entire margin. In Scalaria (fig. 



