380 REVIEWS—GEOLOGICAL EVIDENCES OF MAN’S ANTIQUITY. 
casion to allude again, in the sequel. At present, we may observe, 
that, with the exception of a few reptiles of comparatively low station, 
fishes appear to have been the most highly organized vertebrates’ or 
leading forms of paleeozoic development. These fishes, even those with 
bony skeleton, had, throughout, unequally-lobed tail-fins; and their 
scales (when present) were of a solid osseous character: a peculiarity 
of structure now all but unknown. 
A third epoch of the Earth’s history, the second of its great life- 
periods, is characterized by a remarkable development of reptilian forms 
of varied and high organization. Some of these belong to marine, na- 
tatory types: frequenters of the open ocean; representatives, not in 
structure, but in character, of the great predatory sharks of modern 
seas. Another presents a winged, bat-like structure, and its species 
are amongst the most curious of extinct forms ; whilst carnivorous and 
herbivorous mammals, as now existing, were represented in their func- 
tions by other reptilian types of this Mesozoic Age. Combined with 
these, and equally characteristic of the period, are numerous Ammon- 
ites, and other related cephalopods with foliated or highly complica- 
ited shell-partitions. All of these, and other peculiar types—reptilian, 
molluscous, &c.—became extinct with the closing of the geological age 
in which they had their being. But in addition to these modifications, 
foreshadowing, as it were, the advent of a higher time, a few rare-and 
more or less obscure indications of mammalia occur amongst the or- 
ganic remains preserved in Mesozoic rocks. The best known appear 
to present characters most nearly allied to marsupial or didelphian 
mammals, the lower of the two great: parallel series into which the 
mammalian class admits of being sub-divided. In this age also, a re= 
markable change occurs in the representatives of fish-life. Homocer- 
cal forms appear; and a little later, the rapidly diminishing ganoids 
are all but replaced by teleosteans of modern type.* 
Then another scene appears, and the new geological period heralds 
the dawn of that condition of Nature which we now see around, us.— 
Reptiles form no longer the great leading types of the animal world. 
The strange creations of the Mesozoic day have all disappeared, and 
the Earth is now abundantly tenanted by representatives of a higher 
class, typifying all existing orders of Mammalia save that to which 
* Tt may be observed, for the information of the general reader, that amongst the few re- 
maining ganoids now in existence, the Lepidosteus or ‘ gar pike’ of the lakes and rivers of 
North America, is one of the most characteristic examples. Specimens, easily distinguished 
from other fishes by their enamelled and rhombic scales, may be seeh in any museum, 
