CATECHISM OF CONCHOLOGY. 15 



the space on the other side of the hinge ; supe- 

 rior, the space between the anterior and posterior 

 parts. 



Q. What is the cardo or hinge ? 



A. That part of the circumference in which 

 the valves unite, or are attached to each other. 

 It forms the thickest region of the shell, and is 

 inwardly furnished with one or more teeth : it is 

 said to be compressed when it is formed of one 

 compressed tooth ; lateral when placed on one 

 side of the shell : reflected, when its edges are 

 folded over the exterior margin ; terminal, if si- 

 tuated at the extremity of the shell ; and trun- 

 cated if the beaks of the shell appear to have been 

 transversely cut off, and the teeth of the hinge 

 fixed to this part. 



Q. What are muscular impressions ? 



A. Marks made by the muscles with which 

 the animal adheres to the shell, as in the common 

 oyster. 



Q. What is the Dens, or tooth of a shell ? 



A. It is an acute projection within the hinge. 



Q. What is meant by the Intestinum ? 



A. Internal ligature, or membranaceous tube, 

 B 2 



