62 Beautiful Shells. 
the shells on Plate IV., which are the Perspective 
Solarium (S. perspectivum), Fig. 5, the generic 
name comes from sol—the sun, and viewed per- 
spectively, that is, in such a position that the whole 
top of the shell is at once presented to the view, 
looking like a flat surface, it presents a circular 
appearance, marked with rings and rays like repre- 
sentations of the sun sometimes do. 
The Variegated Solarium (8. variegatum), Fig. 6, 
is a small but very pretty shell, somewhat rare. 
The mollusk is remarkable on account of the 
singular shape of its operculum, which differs from 
that of all other species; it is of a cone-shape, and 
covered from top to bottom with what are called 
membranous lamellz, that appear to stand out like 
little shelves winding up spirally. This singular 
form of opercul™m has been long known to natu- 
ralists, but it is not until lately that they have 
discovered to what species of testacean it belonged. 
Let us here explain that operculus is the Latin for a 
cover or lid, 
