4 THE NAUTILUS. 
is an affinity between these so-called varieties and the species men- 
tioned, I have failed to discover it, though in possession, perhaps, of 
every form of the shells in question known to science. 
Certain writers also claim that the difference between O. irisans 
and 0. textilina Lam. is merely varietal. Possibly this may be 
true; still, the facts do not appear to favor any such conclusion. 
On the contrary, the characters exhibited by large numbers of each 
clearly show them to be specifically distinct. 
It is just possible that intervening forms linking the two together 
are known, such for instance, as those uniting the typical O. irisans 
with its admitted varieties O. ze/anica Lam., O. tremulina, Lam., 
and O. erythrostoma Lam. (Fig. 2), but if so they are certainly ab- 
sent from the several large collections of Olives belonging to mem- 
bers of the American Association of Conchologists and the Phila- 
delphia Academy of Natural Sciences. These are but a few samples 
of the difficulties at present barring the way to a thorough com- 
prehension of the specific relationship of the various members of 
the genus. The presence of such obstacles, however, should be to 
the earnest student more of a pleasure than an annoyance, since 
any effort for their removal will surely give him ample opportunity 
to exercise both his judgment and powers of observation. Despite 
the individual vagaries referred to, the genus is a thoroughly at- 
tractive one, many of the species, indeed, being unsurpassed in 
Fic. 4 O. eryptospira Ford. Fia. 5. 
