944 THE AMERICAN NATURALIST. [VoL. XXXVI. 
Parallelism. — There are perhaps few if any classes of inver- 
tebrates which equal that of the Gastropoda in illustrating the 
law of parallelism of development. In the Gastropoda similar 
features constantly arise independently in entirely distinct 
series ; and since these features are generally used as a basis of 
classification, it follows that our present system of classification 
is in great need of revision. If we represent the natural sys- 
tem of classification by the customary tree and its branches, 
and then pass a more or less warped plane through the upper 
part of this tree, intersecting each branch at the same relative 
stage of development, we obtain a number of scattered points 
where the plane and the branches intersect. If we consider 
these points species, and group all the neighboring and perhaps 
Some distant points into genera and so on, we will get very 
much what we have to-day in the classification of marine 
gastropods. In point of fact, we have only one episode in 
each of the large number of distinct phyletic series, and what 
we mistook for relationship is only a resemblance in a parallel 
developing series which has been cut at the same stage in 
development. Thus it is clear why the customary mistake of 
placing the recent Cyrtulus serotinus (Figs. 17, 17 2) with its 
parallel, the Eocene Clavilithes, is so generally made. Both are 
phylogerontic members of entirely distinct phyletic series, but 
they have reached the same stage in development. Again 
Fusus, known only in the Eocene of Europe, and in this country 
only from the Miocene on, has its close parallel in Pseudofusus 
and other genera in the American Eocene. Here the same 
type of form is developed, — a very simple matter, — but, as 
shown by the life history, the two types are widely apart 
genetically. Again, all gastropods with stromboid lips are placed 
with Strombus, a proceeding which has no warrant from a 
phyletic point of view. The common proceeding of classing all 
loose coiled or non-coiled Paleozoic gastropods under Platyceras 
has likewise no warrant from a phyletic view point, though it 
must be confessed that this is a convenient method when we 
do not know what else to call them. Thus, without multiply- 
ing examples, we may sum up the result of our studies in the words 
of Hyatt's Law of Morphogenesis: «A natural classification 
