40 CATECHISM OF CONCHOLOGY. 



may be readily known by having one of the 

 valves perforated. This perforation is for the 

 emission of a ligature, by means of which the 

 animal adheres to extraneous substances; and 

 thus protects his brittle shell from being injured 

 by the agitation of the waves. 



Q. Will you have the goodness to describe 

 the general appearance of the shell ? 



A. The shell is inequi valve, one valve flattish, 

 the other gibbous at the base, with a produced 

 or projecting beak, generally carved over the 

 hinge, which has a prominent internal muscular 

 impression, and a side tooth placed within ; but 

 in the flat valve, and on the extremity of the 

 margin, there are two long rays for the base of 

 the animal. 



Q. Are the transparent shells of any use ? 



A. The ingenious Chinese use them as sub- 

 stitutes for window glass. 



Q. What has given rise to the peculiar deno- 

 mination of this genus ? 



A. The similarity which some of its species 

 bear to an antique lamp. 



