THE NAUTILUS. 719 
distinguished by size, proportion, color, habits, and relations to sur- 
rounding objects and circumstances.” Like many things which we 
understand very well, the word is difficult to define. It is almost 
impossible to say just what differences are required to constitute a 
species or a variety. Perhaps so far as the study of conchology is 
concerned this definition will answer: A mollusk which differs from 
all allied forms by certain distinct constant characters is entitled to 
specific rank. Asa friend remarked to me: “It is not so necessary 
that the differences between species be great as that they are con- 
stant.” Any character or characters of real value that are always 
present on a shell ought to entitle it toa name; while no matter how 
marked they may be in individuals, if they imperceptibly fade into 
those belonging to what have been considered to be other species, 
they are worthless for purposes of classification. The merest novice | 
who has given any attention to the subject, either collecting or 
examining cabinets gf shells, knows something of how individuals of 
aspecies vary. This variation is very often produced by the cir- 
cumstances by which a mollusk is surrounded,—locality, depth and 
condition of water, different kinds of soil and bottom, height of 
elevation on mountain sides, climate and the like. Baron von 
Tiesenhausen states that Helix cingulata, a smooth shell, is found in 
the valleys of Austria, H. cingulata var. colubrina, a little mottled 
and sometimes slightly ribbed, about half way up the mountains, and 
H. gobanzi, which is only perhaps a strongly ribbed form of 
cingulata, lives near their summits. Fasciolaria tulipa, when found 
in quiet muddy bays is a coarse shell with strongly-marked revolving 
ridges, of a dirty brownish or ash color and scarcely variegated at 
all ; and is in every way inferior to the much larger, finely developed, 
smooth and handsomely variegated specimens taken in the open 
sea. Natica duplicata, from the vicinity of New England, is a coarse 
shell often flushed with brown or brownish-yellow, while specimens 
from the open water in the Gulf of Mexico are smooth and polished, 
livid in color, or even almost white. The same shell, though, when 
found in brackish water on the Florida coast, is more like the New 
England form, but is never brownish in color that I have seen. 
Cyrena floridana is a most variable shell even when a number are 
taken from the same bed; so much so that Conrad who just named 
it, subsequently gave to other very different specimens the appellation 
of C. protexta. In color it ranges from a dark purplish crimson, 
through purple and pink to white, and individuals may be found of 
