1888. J 
21 
[Hyatt. 
An interesting result of this agreement between chronology and 
taxonomy is, that the successive faunas of the Lower Lias also 
present a similar order. Thus, the faunas of the lowest beds, the 
Planorbis and Laqeuus, or as I have called it, the Caloceras bed, 
contain in preponderating abundance the forms of the radical 
stock ; the Angulatus bed is characterized by the progressive forms 
of the Schlotheimian branch and by numerous radicals of progres- 
sive series, the Lower Bucklandi bed by the general blooming out 
of progressive forms in the normal series, and the Upper Buck- 
landi or Geometricus bed by the incoming of degenerate forms in 
these same series, and the beds above this by the advent of de- 
generate series and the more marked degeneration of species and 
dying out of the whole family, with the exception of two species of 
Oxynoticeras that still survive in the Middle Lias. 
The life-history of the whole family is, therefore, from every 
point of view, comparable with the life-history of any one individ- 
ual. The shell of the individual has a period of early stages of 
growth during which it passes through progressive stages which, 
according to Haeckel’s nomenclature, may be styled the anaplas- 
tic stages, the adult or fully developed progressive stages are 
equivalents of his metaplastic stages, and the stages of decline 
can be similarly named the cataplastic stages. Each series, as we 
have just said, has similar stages or periods of evolution in time, 
and the entire group is similarly related. Haeckel has named these 
three in a general way, the epacmatic period of progress, the ac- 
matic or fully developed period in the history of a series, and the 
paracmatic, or period of the evolution of degenerate forms. The 
author pointed out these phenomena and their agreements among 
Cephalopoda, in the same year that Haeckel published his views, 
but did not propose an appropriate nomenclature. 
The successive faunas may now be similarly classified and ar- 
ranged to accord with the ontology of individual and the evolution 
of the group, and styled the Epacmatic faunas, the Acmatic faunas, 
and the Paracmatic faunas. The Epacmatic faunas occupied the 
Planorbis, Caloceras and Angulatus beds, the Acmatic were in the 
Bucklandi beds, and the Paracmatic characterized the Tubercula- 
tus, Obtusus, Oxynotus and Raricostatus beds. So far as the 
Arietidse are concerned, there is no justification -for any chronolo- 
gical subdivision of the Lower Lias faunas unless it be into three 
parts as indicated by these relations. 
