I893.J 115 [Hyatt. 
teristics of this class do run a certain limited cycle of changes and 
then disapjiear. In that case investigations would be required to 
establisli the facts and also to determine whether they should be 
considered as coming under the head of bioplastology or ctetology. 
Within my limited exj)erience there are no fixed characteristics 
which do not obey the laws of bioplastology. Those appearing 
sporadically in individuals or those plainl}^ due to locality or some 
habits, which are not perpetuated in the i-ace or phylum after 
the causes that gave rise to them have ceased to act, have l)een 
moi-e extensively studied b}^ others and I must leave such ques- 
tions to them. 
Relations of the Nomenclatures of Taxonomy and 
Bioplastology. 
Prof. J. F. Blake proposes^ abandoning the terms "genera" 
and "s])ecies" and apparently the whole terminology of taxonomy, 
and it is evident that some discussion of the relations between 
binominal nomenclature and that already employed in bioplas- 
tology or pi'oposed in this paper is necessai-y. 
This learned authority has given generous praise to my work 
and his good opinion has been very gratifying to me. He has 
also been justifiably frank in his criticisms, and on some ])oints, 
as upon thiit of nomenclature, we are not in accord. 
In support of the revolutionary opinion cited above he makes a 
distinction which does not in my opinion exist. Thus, after 
speaking of the distinction between the genus of contemporaneous 
species and the lineage of "successive forms", he states, "Unfor- 
tunately Hyatt still uses the word genus at great risk of confu- 
sion for a single genetic line," and then quoting from my Genesis 
of the Arietidae he adds, "The unit of classification is, therefore, 
not the species but the genus ; in other words, it is tlie smallest 
natural group which is genetically connected, and in which a more 
or less complete cycle of forms or species may be traced. In such 
a system, also, certain radical forms which do not show the usuiil 
morphogenetic cycle may occur. These may have a closely 
allied and inseparable series of varieties, which cannot be distrib- 
1 Evolution and classification of Cephalopoda, Proc. geol. assoc, v. 12, p. 80 et spq. 
and 295, April, 1892. 
