SOLARIUM 



TESTA subdiscoidea, late umbilicata, spira obtusfe 

 conica, apertura trapeziformi, peritremate tenui, 

 acuto, umbilico margine spirali crenato; oper- 

 culo corneo, siib-spirali. 



The shell commonly called the Staircase Trochus has, from 

 the time of its being first known, been deservedly cele- 

 brated among collectors, on account of the beauty and 

 symmetry of its external form and its elegantly crenated 

 spiral umbilicus. This was placed by Linne among the 

 Trochi, to which indeed it appears to us to be nearly 

 related. It has, however, been since separated, and forms 

 conjointly with its more closely related species the modern 

 Genus Solarium. This we have adopted without hesita- 

 tion, because we find a number of shells distinguished 

 specifically, but yet agreeing in certain generic charac- 

 ters which therefore in our view, form a natural genus. 



The shells forming this Genus are usually of a some- 

 what discoidal form, with an obtusely conical spire, the 

 lower edge rather sharply angular, and the umbilicus 

 broad and deep : they vary, however, occasionally, in a 

 slight degree from this general form, having the spire 

 sometimes of a rather more lengthened conical form, the 

 basal edge more obtuse, angular, and the umbilicus broad 

 and deep. The umbilicus has, in almost all instances its 

 spiral lower margin strongly and closely crenulated, 

 though occasionally this also is subject to some variation, 

 as in the S. patulum, for example, in which this spiral 

 lower margin of the umbilicus has only a few small grains 

 placed here and there at a distance from each other. The 

 aperture is trapeziform, with more or less rounded angles, 

 and a thin sharpish peritreme. A thin horny epidermis 

 covers the shell in its natural state; this is either very 



