VARIETIES OF NASSA. 69 
an apex of a reddish tint. In form they are found to resemble 
each other in many of the varieties, the principal distinctions being 
the red lines surrounding the N. glans, which are altogether wanting 
in any specimen of N. papillosa I have seen. At the same time it 
must be remembered that we have varieties of the former shell 
without a trace of the red lines. 
The papille are for the most part in longitudinal “series, and 
appear as protuberances on the ribs, very similar to the shells of 
N. subspinosa, Lam. <A small white or yellowish shell before me, 
with a rufous stain on the back, coronated at the sutures, and with 
the ribs very irregular, is so like the N. papillosa in form, texture, 
colour, and striation, as to render the opinion of its being anything 
but a variety of that shell next to impossible. 
The difficulty in understanding how it is possible for these 
twe shells—apparently so different in external appearance, the one 
being smooth and the other strongly papillose—to be varieties of 
each other arises from the want of a little careful comparison. The 
following diagram will show how they unite in the first shell, to 
which the slightest pretension to specific distinction can be applied, 
viz., N. hirta, Kien, ‘There is no break in either of the lines of the 
descent, therefore the line of separation appears to be open at the 
top of the triangle. Over this we have placed N. reticosa, J. Sow., 
from the Crag, one of the oldest and most variable shells in the 
whole genus Nassa. My reasons for placing the alliances in this 
order is very simple. The Nassa gemmulata, Lam., shows a change 
from the ribbed and cross-grooved shell, having the external sculp- 
ture very similar to the shell in question completely changed into a 
variety with round papille. Supposing that the two shells, the 
smooth and the papillose, have sprung from the old N. reticosa, 
_ J. Sow., then we might expect to find the papille to have been 
developed in the squares of the reticulated varieties, similar to that 
which has taken place in the case of N.gemmulata, Lam. There is not 
the slightest reason to suppose that because we find the coronation, 
ribs, and general sculpture developing from the smooth form that 
we should not also find instances in which the exactly opposite 
development, viz., from the sculptured to the plain, takes place. 
