1854.] OF THE ROYAL INSTITUTION. 431 
living or extinct as yet described, so far as our knowledge extends — 
and there is a consistency in its co-ordination that suggests the 
probability of our being acquainted with its extremes,—the creation 
of the fauna and flora of the oldest Paleozoic epoch would seem to 
be the primordial and the appearance of man the closing biological 
events. 
When the assemblage of characteristic Neozoic groups or genera 
is contrasted with that of the Paleozoic, there we find that the 
concentration of a maximum development of generic types towards 
the earlier stages of the one and the later of the other great period, 
includes something more than a mere numerical profusion of generic 
ideas. The two great manifestations of creative intensity are in 
opposition, or contrast, and respectively substitute each other ; 
groups that are parallel within their sub-kingdoms or classes taking 
the place of each other and playing a corresponding part in the 
economy of nature. This replacement does not depend on the sub- 
stitution of a group of higher organization during the latter epoch, 
for one of lower during the former. Where there is such a substi- 
tution it must be regarded as an accident; for the rule is not 
general nor can it be held good except for a few instances. 
A few leading examples of the substitution of group for group 
during the contrasting epochs are cited in the following table and will 
illustrate this point better than a mere abstract statement. 
Neozoic. PaLz#ozo1c. 
Cycloid and Ctenoid Tubes . . Ganoid and Placoid Tubes. 
Malacostracous Crustacea . . . Entomostracous Crustacea. 
Dibranchiate Cephalopoda. . . Tetrabranchiate Cephalopoda. 
Lamellibranchiate Sea . .  Palliobranchiate Acephala. 
Echinoidea . . . .  Crinoidea. 
6-starred Corals . . . . . . 4-starred Corals. 
If we were to shew by means of a 
detailed diagram the relations in each 4 2 Maximum 
of these groups of the development of © Xo develop. of 
generic types to time, we should sym- ©& Paes poner 
bolise it by a cone or apyramid, the 2 ae TREE. 
base or fullest portion of which should 8 © Mini 
. o ~ Inimum 
be turned respectively towards the 2 \ produc. 
commencement of the Paleozoic, or . } tion of 
termination of the Neozoic epoch. The 4 } generic 
last example given will shew this 2 4. types. 
strikingly, though in most instances » a 
the groups interlace. 8 aa Masaee. 
Relations of this kind may be mani- & << of 
fested in alow degree, even within the & D 9 generic 
range of a single group. Ao PIPES 
