OF CONCHOLOGY. 35 



" On the contrary, a reversed shell 

 when placed in a perpendicular posi- 

 tion, has its spiral volutions in an 

 opposite direction to the motion of 

 the index of a watch, or a clock, or to 

 a common screw ; and, in fact, resem- 

 bles what is usually termed a sinistra!, 

 or left-handed screw. These have 

 their aperture on the left side, or op- 

 posite the left hand of the person, 

 holding the shell with the mouth 

 downward ; and the opening is oppo- 

 site the sun's apparent motion. Plate 

 3d, h>. 13th. 



base or bottom. It is also admitted, that when the shell is 

 placed on its base, with the aperture facing the observer, that 

 this is termed the front — plate 3d, figures 7th and 8th, &c. ; 

 and that placed with the aperture from the observer, it is 

 called the back — plate 3d, figures 9th and 10th. When all this 

 is admitted, it appears to me that the side in which the aper- 

 ture is situated, is unequivocally the left side, and the opposite 

 extreme the right. Surely if a man is placed on his feet, with 

 another facing him, the one could not call the side fronting 

 his right side, the right side of him opposite. If any thing, 

 whatever it may be, has a top, base, and proper front, it must 

 also have a proper right and left side ; and what I have de- 

 scribed as such, I think will be found to be so. 



