CATECHISM OF CONCHOLOGY. 47 



ihg of the terms digiti> dorsitm, epidermis, and 

 labium. 



A. ReadiJy. Digiti signifies clatos, or finger- 

 like divisions of the outer lip. Dorsum is the 

 back of the shell, or the upper part of the body 

 when laid on the aperture. Epidermis, skin, a 

 raembranaceous covering of the shell, found on 

 some but not on all species. Labium interim , 

 lip, the internal or columella margin of the 

 aperture : exterius> outer margin of the aperture. 



Q. What is an operculum, or lid. 



A. It is a plate or door, with which some 

 species close the aperture of their shells ; it is 

 either of a horny, testaceous, or membranaceous 

 substance. 



Q. What are the radii, or rays ? 



A. They are elevated striae, or lines, tending 

 from the centre to the circumference. 



Q. Is not the spira, or spire, the upper whorls 

 of the shell ? 



A. Yes: and the suturae, or sutures, are the 

 spiral lines of connexion between them. 



Q. What is the Latin appellation of a shell ? 



A. Testa. 



