40 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 
smooth. The variability of colow-marking is notorious ; but strange 
though it may seem, and opposed as it is to current views as to their 
diagnostic value, I find that colour-markings, despite their enormous 
ariability, are really of great assistance in the discrimination of the 
types of Columbellide, and the same remark apples also to other genera. 
If a careful study be made of the markings of even the most variable 
forms, it will, as a rule, be possible to demonstrate the existence in 
each species of a definite and characteristic colour plan or system of 
marking, from which all the patterns, often very diverse, represented 
in the series may be derived. The protoconch is a feature possessing 
characters of great diagnostic value: forms otherwise almost identical 
In appearance may often be at once distinguished by a comparison of 
the embryonic whorls of their shells. The periostr acum, again, affords 
characters of importance, but it is usually neglected in the description 
of a species; the same is true of the operculum. In some cases I have 
found that the easiest way to separate living specimens of closely 
allied forms has been to observe the external characters and habits 
of the animal. Although there is no very great variation, such as is 
met with in some other families, in the form and arrangement of the 
lingual teeth of the Columbellide, yet there generally are sufficient 
differences in their number, spacing, and dimensions to render the 
characters of the radula of considerable importance as a means of 
distinguishing species. 
The Classification of the Columbellide.—The large number of species 
meluded in this family appear to form an exceedingly homogeneous 
group, and to exhibit but few characters which can be regarded as 
of sectional value. This similarity of type is perhaps only what 
might be expected, in view of the comparative newness of the group ; 
but, on the other hand, indications are not wanting that the similarity 
is more apparent than real, and further rese: arch, especially if this 
be directed to the structure of the soft parts, may well reveal quite 
unexpected divergences of type. At present, however, it is a matter 
of considerable difficulty to satisfactorily subdivide the Columbellidee 
into genera and subgenera; and the difliculty has been much increased 
by the misdirected efforts of the mere conchologist. Numerous sectional 
names have been proposed from time to time, but very few of these 
have any real worth, and whatever value a section may have originally 
possessed, its true significance has in most cases been entirely lost 
sight of by subsequent authors, and species have been scattered about 
among the various genera and subgenera in an amazingly haphazard 
fashion. 
In the present state of our knowledge I do not think that we are 
justified in attempting much more in the way of classification than 
the mere grouping of species around certain central forms: we may 
thus speak of the Co/umbella mercatoria group, of that of C. terpsichore, 
and so on. For the present I am referring all the forms to Colwnbella, 
and shall leave the question of their more precise classification for 
future consideration ; and, as a necessary corollary, 1 am not proposing 
new trivial names where by the strict application of the law of 
priority such would appear to be demanded. 
