ON THE 
VARIETIES OF THE ‘SHELLS 
BELONGING TO THE 
feos, N Ao SA, baw. 
By F, P. MARRAT. | / 
PMP iy OD: UC Tl ON: 
Tue study of varieties in the genus Nassa has achieved one great 
object,—it has taught us the whole details of the plan on which 
the external ornamentation of shells has been elaborated. The 
whole of the variation, from the smooth shell to the most distinctly 
sculptured examples, is plainly to be seen as effected through 
almost imperceptible gradations. 
An attempt might be made to show the lines of divergence by 
means of a diagram, but in all the instances in which this has been 
done in other branches of Natural History the results have not 
been satisfactory. 
Neither a tree-like form nor any genealogical chart could he 
made to represent varieties in anything like the ramifications in 
which they occur in Nature, nor could we hope to succeed in such 
an undertaking without being able to procure a very large addi 
tional series of species such as would enable us to follow more 
closely the missing links in the scale of affinity. 
For the most part, I do not regard a peculiar character possessed 
only by a single specimen as constituting a “variety.” Even 
“intermediate links” between allied forms are generally repre- 
sented in my series by two, three, or more, closely similar specimens, 
