EXPLANATION OF TERMS, 393 



or truncate as in Buccinum ; in the two latter it 

 thus gives place to a notch, but in all these instances 

 it is that part fitted for the protrusion of the long 

 cylindrical siphon possessed by all these animals. 

 This part, also, constitutes the base of the shell. Be- 

 sides this, there is in many of the mitres, Stromhi, 

 and other predaceous genera, another channel or 

 groove, placed in the interior of the upper part of the 

 aperture, the use of which has not been fully ascer- 

 tained. 

 Cancellated, When the surface is marked by striae or 

 lines, which cross each other at right angles. 



Cardinal teeth of bivalves, are those placed immediately 

 beneath tbe bosses, and between the lateral teeth 

 where such exist, as in the common cockle. 



Carinated, or keeled. Furnished with an elevated, and 

 often a sharp ridge, either on the surface or margin 

 of the shell. 



Chambered. Divided internally into compartments, as 

 in the testaceous Cephalopoda, or Nautilus. 



Clavate, club-shaped. One extremity being slender and 

 pointed, the other thick and obtuse. Many of the 

 zoophagous genera, as Cerithium, &c. are peculiarly 

 strong examples. 



Columella, or Pillar. The internal support of most 

 spiral shells, round which the whorls convolute : it 

 is not present in Solarium, Delphinula, the typical 

 Scalar ia, and a few other genera ; all of which, in 

 consequence, have the umbilicus so deep, that it ex- 

 tends to the apex or top of the shell. The basal 

 portion of the columella generally forms the support 

 of the inner lip, and always that around which the 

 plaits are disposed, as in the Volutes ; it is some- 

 times greatly thickened, as in Ancillaria, and all the 

 Olives. 



Concentric. Stripes, grooves, or other external marks 

 indicating the progressive enlargement or growth of 

 the shell : hence those indented stripes or striae in 



