RED AND YELLOW SUX-BEAM. 
The Blue Sun-Beam, however, is of the 
Cunei genus, having ciissimilar sides ; while 
the Red and Yellow Sun-Bcam, which we 
have exaclly delineated, is of the genus first 
described, having both sides equal. 
The colours are more or less brilliant in dif- 
ferent shells : and, not unfrequently, the yel- 
low is seen degenerated into a very pale straw 
colour, or even white itself: while the red 
also glows, occasionally, in all the varied and 
evanescent hues which we find depi6Led on the 
clouds ; sometimes blushing with the deepest 
and most brilliant crimson, and sometimes 
barely tinged with a scarcely perceptible pale 
pink. These observations, indeed, are appli- 
cable to shells in general, which differ asto- 
nisliingly in the richness of their colours, espe- 
cially when they are not originally taken with 
the living animal ; and, in bivalves, it may be 
remarked, once for all, that the under shell is 
always pale, and often quite colourless. 
