SPIRAL SHELLS. 1 1 



to cover his head in the hour of danger. How well has 

 he combined the utile cum dulci ! the comfortable with 

 the ornamental ! Its general form is that of a cone of 

 much regularity, but with an oblique base, and perhaps 

 you may be surprised to learn that this conical form is 

 but the result of the winding of a very long cone upon 

 itself in a spire. But if you examine a dead shell with 

 care, you will see that it is so. Supposing you had a 

 very long and slender hollow cone of plastic material, 

 and, beginning with the acute point, you twined the 

 whole upon itself, descending in a spiral form, you 

 would have the representation of a turbinate shell, 

 which, by a little gentle pressure of the fingers, might 

 be moulded, without at all losing its essential character, 

 into the exact shape of our Trochus, in which the pro- 

 gress of the spire can without difficulty be followed as 

 well by slight inequalities of surface as by the arrange- 

 ment of the colours. 



It is one of our showy shells. This specimen before 

 us has for its ground colour a chaste, cool grey, occa- 

 sionally varied with tints of reddish buff, but most 

 conspicuously adorned with a series of large and regu- 

 lar spots of purplish crimson running along the lower 

 angle of the spire from the base to the summit. Each 

 of these spots passes off into an oblique line above, the 

 repetition of which augments the beauty of the pattern. 



