26 



INTRODUCTION. 



extremity, it is said to be emarginated. When the edge of 

 this notch is expanded, and drawn out in the form of a beak, 

 it is said to be canaliferous, or to have a canal. When, in 

 addition to this, the lips are thickened and contracted poste- 

 riorly near their junction, and drawn out so as to form a 

 groove, it is said to be bi-canaliculated, or to have two canals. 

 The anterior canal is said to be long or short, according 

 to the proportion which it may bear to the rest of the shell. 

 Thus the canal of Ranella ranina (fig. 393 in the plates), may 

 be described as short; while that of Murex haustellum, 

 (fig. 396, pi.) is long. When it is wide near the aperture, and 

 becomes gradually contracted towards its termination, it is said 

 to be tapering, as in Pyrula (fig. 388, pi.) ; when the termi- 

 nation is sudden, it is described as truncated. If, on placing 

 the shell upon a plane, with the aperture downwards, the canal 

 is seen to rise upwards, it is recurved. In Buccinum and 

 Nassa it is turned suddenly over the back, and forms a short, 

 curved elevation ; it is then described as recurved and vari- 

 cose. If the edges meet, so as to form a tube, it is said to be 

 closed, as in some species of Murex and Typhis. The pos- 

 terior canal is, in some cases, free, or standing out from the 

 spire, as in some species of Ranellse; while in others it is 

 decumbent, running up the sides of the spire, as in Rostellaria 



(fig. 402, pi.). 



Canals. 



Fig. 51, Fasciolaria, truncated ; 52, Nassa, recurved, varicose 

 53, Cerithium, recurved ; 54, Typhis, closed. 



