
922 THE AMERICAN NATURALIST. (Vor. XXXVI. 
gastropods. Such accelerated type of protoconch is particularly 
characteristic of the Fusidze, though not confined to them. In 
some members of this group, Ze, Fusus caloosaensis and its 
congeners, the ornamentation of the protoconch begins very 
early, showing extreme acceleration. This is also true of Fusus 
apicalis Johnson. Neither of these species is a true Fusus. 
The classificatory value of the protoconch of gastropods has 
not generally been recognized, Dall, so far as I know, being 
the only author who has made extensive use of it. It is, how- 
ever, apparent that if our classification is to express genetic 
relationship, this, the earliest formed portion of the shell, 
demands a careful consideration. It is generally conceded 
that organisms of a common ancestry are more nearly alike 
in their earliest stages of development, differentiation becoming 
more and more marked inlater stages. This is to be expected 
if the law of recapitulation of ancestral characters is accepted, 
for then the earlier stages must more nearly represent the 
features of the immediate ancestor in any particular restricted 
group. Furthermore, the smaller the taxonomic group, the 
more nearly identical must be the earlier stages, since in a 
small group the members have not become widely separated 
from their common ancestor. Thus, while the initial whorl 
of the protoconch does not differ widely, except in size, in the 
majority of gastropods, indicating the characters of the more 
distal radicle of the class, — ż.e., the naticoid ancestor, — the 
whole character of the protoconch must be considered in the 
determination of the more immediate relationships.  There- 
fore, I believe it is not too much to say that the protoconchs 
of all the species within a given genus should agree as to their 
essential characteristics, and that no species can be considered 
congeneric in which the protoconchs show a radical difference. 
Thus, as will be shown in a forthcoming memoir on Fusus and 
some of its allies, the American Eocene species of Fusus do not 
show the typical Fusus protoconch, but some have a protoconch 
like that of many species of Pleurotoma and like Levifusus 
trabeatus (i.e, Fusus meyeri, etc.). Others again have the pro- 
. toconch of Fulgur (Fusus guercollis, etc.), of which group they 
are the Eocene ancestors. The species referred to have adult 
